I'm not concerned with the soap opera of day to day intrigues, accesses, individual party standing, etc. I'm concerned with long term party viability. Mao managed to secure the allegiance of large numbers of countryside people, enough to prevail. Can other factions that are more amenable to Stalin's dictates have the same traction? I assume, no, not the same; any faction that owes more to foreign influence than local will smell of it and repel local support to some extent--thus I was suggesting Stalin trying harder and succeeding in bumping Mao off as a means of keeping his control over the Chinese movement--at the cost of losing effectiveness, giving KMT a better chance.
OTL the Chinese CP faction that did obey the Kremlin was given orders to cooperate with the KMT, and Chiang took advantage to try to exterminate them all. That's generally how Stalinist-obedient factions fared under Stalin's orders; he prioritized keeping control which meant promoting hacks over local leaders who had effective grass roots traction, and trying to govern the pace of revolution either in accordance with some half-baked Party line of the moment out of phase with on the ground realities, or often governed by balancing appeasement of pro-capitalist interests to smooth Soviet relations with Western powers, which inherently meant leaving the grass roots revolutionaries keen on seizing every opportunity out to dry. This is presumably why Mao did prevail in the end, ignoring Kremlin direction and doing what he thought best to advance CCP chances in China, to hell with Stalin's agenda. This is in fact how all successful Leninist revolutionaries everywhere in the world prevailed, in Yugoslavia (Tito tried to be obedient, but Moscow rarely sent any useful aid and he was on his own practically speaking, getting more help from the British and Americans during the war than from Russia), in Vietnam, in Cuba (Fidel Castro never was formally a Cuban CP member and purged the Cuban Party starting with executing its leader in the early 60s; his brother Raul was his contact with that Party, a junior partner in his personally led movement). And in China! To postulate a non-Communist regime in China one has to nerf the Chinese Communists; Stalin is a help here.
But even with Stalin doing the KMT favors, exactly how does that party get the legitimacy it needs to become the agreed upon leader of China and create some degree of lasting peace? As I understand it, China had fragmented into dozens of regional fiefs controlled by local warlords of diverse theoretical positions that in practice all boiled down to getting on top of a more or less traditional Chinese food chain of landlords, bureaucrats answering to the warlord rather than any central agency, and random capitalist-industrialist entrepreneurs, if I am not mistaken as likely as not to be foreign. The latter gave the Republic of China some sort of zombie-like legitimacy in that foreign investors obviously liked being influential on the powers on the ground, but overall the result was violent chaos, a complete lack of effective progressive vision (beyond merely enforcing the profitability of various enterprises by repressing the workers, who were quite numerous and disposable) and withal tremendous rates of population grown atop a ramshackle economy.
It is obvious enough to me how Maoist cadres got traction in the countryside in a situation like this, and eradicating them would be more than a matter of just killing off Mao. And without such a movement, how will the KMT balance the attempt to gain some grassroots legitimacy versus their commitment to the elites the OTL Maoists credibly were going to fight and overthrow? I can't see how they do otherwise than lean on top-down domination, double down on it until the masses despair of any alternative, and create a hypercapitalist dystopia. Perhaps an unopposed KMT can come under strong central leadership, impose some rough order on the warlord ruled provinces that imposes a sort of sullen interregional peace and steers the warlords from attempts at expanding their personal area of rule and toward kleptocratic participation in regional development instead. None of this results I would think in a situation objectively less terroristic and more prosperous for the masses than OTL Maoist rule with all its failings and brutality; it seems unlikely it could result in more effective per capita development.
The ATL does not have to provide a humane and democratic order to be sure! Only explain how the hideous mess is politically stable and capable of dealing with rival powers as effectively as the PRC did OTL.
Will the USA ally with such a China? Well I suppose we would. China after all borders on the Soviet Union. This helps explain why the Soviets were so keen to see China revolutionized. Without a deep POD early in or before WWII, it is hard to see how at least some Chinese territory does not fall to Red Army occupation and once occupied, how it would ever be handed back to an anti-Communist regime. That merely moves the border out from old Soviet and Mongolian borders of course, it does not do much to shorten the border. However it would buy the USSR a buffer zone comparable to Eastern Europe at the other end of the continent.
The Republic of China that might wind up allied to the USA then would probably be much shrunken, perhaps even driven out of the north of China completely. Let us suppose otherwise, that the eastern part that was densely settled would remain, with US aid, in KMT hands, while west and north Soviet occupation shelters a number of puppet SSRs of low population and development, swarming with forward Red Army bases and barely able to sustain these, let alone meaningful development.
Sure, there might never be a Korean War--although actually Soviet forces were poised to invade Korea directly at the end of WWII and probably would do so in the ATL, indeed American commitment to the RoC might divert the forces occupying southern Korea and hand the whole peninsula over to Soviet clients wholesale. There might instead be a Manchurian War, or a China War, trying to recapture core Chinese territory from Soviet control, or Soviets attempting to hold extensions of their power at dubious length from their core lands.
That instead of Korea there would be some Far Eastern alternative flashpoint seems almost certain to me. The Cold War might be shortened all right, by turning into a hot WWIII where Stalin lacks the plausible deniability he had OTL (in fact, I believe both that the South Korean authorities fostered by the US had their own loose cannon culpability in feeding the flames in Korea, and that the NK and Chinese leadership both defied Stalin in piling on too--neither Washington nor Moscow masterminded it, and that was one reason why over time it was possible to force a negotiated settlement--both superpowers wanted none of it, it was a matter of reining in their clients). In this ATL, we might soon have US military forces, with or without a UN mandate (impossible to get unless the Soviets walked out in a huff over other matters as they did OTL) fighting Red Army directly, and this could soon escalate into general war on all fronts, Europe wracked by terrible conflict once again, and US strategic bombing, now nuclear, pounding the Soviets into radioactive rubble, unless they call for a truce early in that process. (Nuking the USSR and clients until they glow would be a much slower process, since the USA had rather low stocks of A-bombs, and furthermore delivering them would be a matter of enabling fleets of piston bombers to reach interior targets despite vigorous Soviet attempts at interdicting them. It would be possible that relatively few Soviet targets would be destroyed before Stalin or a successor would offer terms for partial Soviet withdrawal. Meanwhile quite a lot of radioactive fallout, including most of the uranium or plutonium installed in the bombs, would be released to the severe detriment of ultimately everyone in the northern hemisphere. The upshot then might not be a short Cold War that goes rapidly hot ending in the destruction of the Soviet Union, but a costly and devastating WWIII leaving both sides still standing, the Soviets somewhat down on one knee to be sure, but both badly battered and with long-term damage lasting generations. And resumption of a new Cold War, even more bitter than OTL for the scale of mutual damage each side inflicted on the other. In this Cold War, the Sino-Soviet border becomes a huge hot zone, stretching nearly inconceivable distances across the most rugged and difficult terrain on the planet, with massive numbers of deployed Yankee and perhaps other Western allied troops salted in bases among huge conscript Chinese forces of dubious reliability (but very large numbers) drawn from a China devastated both by direct Soviet strikes, drained of loyal and well-trained manpower by the war, and poisoned by fallout from strikes in the Soviet east. The KMT regime might lean heavily on US support to remain viable at all, a South Vietnam Saigon regime writ monstrously large; to support our commitment on such dubious terms to something so grotesquely termed part of the "Free" world the USA and Western European nations might have to impose severely authoritarian controls on organization and speech and curtail freedoms across the board, not to mention exact substantial taxes--taxes that ought to be levied on the rich, but the more authoritarian the western regimes become, the less concerned with populism, and the burden would shift heavily onto the populace at large. Which might in turn legitimize Communist opposition underground in the West.
For it to be otherwise, the ATL KMT or whatever third party one might envision must achieve both mass legitimacy and competence pretty early, preempting the warlord period, perhaps effectively stopping the Japanese invasions of the later '30s and thus completely changing the course of history in east Asia long before OTL Pearl Harbor Day. The POD must be in the 1920s, or even earlier, and involve what I would presume to be a highly improbable development of a movement with something for everyone, that preempts both the top-down corruption of the OTL RoC under Chiang and the bottom-up radical populism of Mao. Give us that and perhaps something like OTL WWII goes forward in Europe, maybe the Japanese fight elsewhere than in China, or attempt invasion of China but are thrown out, and the the RoC (or ATL dynasty, or whatever) can keep the borders with Russia and deter a WWIII fight in the late 40s or early 50s. Such a China still must face how to address low per capita incomes, low literacy and general education, low levels of overall industrial development, and do so in the face of a tremendous and growing population it must either check the growth of drastically or expand industry at unheard of rate to get ahead, implying massive resource consumption that expands exponentially.
As I say the ATL author has their work cut out for them to explain China's mere existence as a sovereign power, let alone one peaceful and prosperous to help contain the USSR. To speculate it is a peaceful world with a subdued Cold War strikes me as pretty fatuous unfortunately. I'd settle for a Cold War as tense as OTL.