Except that mass alone is useless - see WwI. If I had a choice between half a million men who were trained, equipped, and prepared to the highest levels possible in 1940, and invading Russia with an army over three and a half million but which has to depend on 625,000 horses - I'm going to take the mechanized army.
"Highest levels possible in 1940" implies either an earlier start to the war (degrading technological advancement due to wartime necessity with the tradeoff of increased real-world training,) or ignoring France and the Benelux and starting Fall Weiss & Barbarossa simultaneously, with slightly more of what was used for the OTL 1940 invasions. In essence, the Heer can do one pretty thrust into Belarus, and fall to pieces between trying to subdue the Poles and fend off the human wave attacks by the USSR.
Half a million, towed by better trucks and SdKfz 251's? They never worked out the reliability issues of the Gewehr 41, so even rushing that is out, and they're still using K98's, MP40's, and MG34's. The early variants of the Panzer IV are possible, however it takes war lessons to improve them to a level that would be able to match the KV-1&2, let alone the T-34.
The German army in 1944-1945 is not "a small army of technicians" trained and equipped accordingly, it's the understrength remnant of a "WWI but with more tanks!" army.
We're not talking OTL current US capabilities by delaying the onset of the war a decade, either. The economic issues are far too pressing. Concentrating tech, arming a smaller number in a better fashion, AND sustaining the economy are nearly as mutually exclusive for Germany as arming millions with inadequate equipment.
Also consider the distraction projects in many directions at this time. To spin up tech further, your POD would need to include consolidation.
So when both sides are using mass, obviously the side which can "systematically (apply) overwhelming force" wins - but that proves nothing on whether a smaller, better German army would have been better off than an army that still lacked the numbers and was under-equipped and under-mechanized.
A smaller Heer would have been better off, in peacetime. Basically, you're proposing the end result of a wank a lot of Germanophiles approve of: A Germany that gets, (via democracy and diplomacy) 1914 borders, plus Sudentenland and Austria, minus Alsace-Lorraine, and integration into a NATO/EU arrangement against the USSR. The POD would probably then have to be before Hindenburg's death.
In essence, a Germany that:
-Gets a charasmatic leader no later than the same time as OTL
-That leader quickly gets passage of an Enabling Act
-Aforementioned leader gets all of Hitler's land gains (minus non-Sudenten Czechoslovak territory, yes, I know that means losing the Skoda works and everything else, but this is for the diplomatic victory,) plus that particular corridor
-Leader is sane enough to step down from a government position and call a constitutional convention.
-Resultant Germany is democratic and exploring alliance with the rest of the West, even considering offering them support in a war against Japan.
Honestly, that's a Germanwank I'd love to read. It's also ASB-tastic.
