I'd argue that the lack of the A6M is actually incredibly beneficial for the Japanese (I'm interpreting this to mean they don't simply navalize the Ki-43, which given the incredibly low landing speed with those fowler flaps would have been relatively doable).
While many have pointed out that the A6M was instrumental in their early offensives, it horrifically hamstrung them later in the war.
The navy was politically powerful, but lacked a replacement fighter to load onto their new carriers they kept trying to build. This tied the Japanese aircraft industry's leg to this crap fighter that had horrible characteristics for fighting a defensive war.
What Japan needed was Ki-44's, Ki-84's, even Ki-61's were better suited for the war despite their detriments.
All of them had excellent diving characteristics (with exception of the Ki-84 to an extent, I'm given to understand the horizontal stabilizers could be compromised at as low as 450mph IAS), good rates of climb through wide altitude bands, excellent rates of roll, good acceleration, and importantly kept responsive controls throughout their flight envelopes.
In other words, they posses the characteristics of being able to quickly build energy through climb and acceleration. They have the ability to convert large quantities of potential energy to kinetic energy through diving. They would retain energy well due to their (relative to the A6M) high top speed, resulting in less power deficit for any given speed above Vmax, as well as relatively low induced drag on the control surfaces. And most importantly, they have the ability to take advantage of all of these previous attributes due to their excellent control response at high speeds.
Why is this important you ask? Well, absent the A6M, it's possible these projects will get more money thrown their way, resulting in earlier deployments. Not to mention prioritization after their combat records begin to speak for themselves.
Additionally, these are the very attributes you should seek when forced to engage a numerically superior enemy, as well as a much better match for the US design philosophy of fighters.
Higher losses for US aircraft lengthens their turn around time between campaigns, especially where more specialized carrier pilots are suffering the brunt of the losses.
And crucially, I believe the stupidly low wingloading requirements will be dropped, or raised on later fighter designs, giving engineers less difficult design constraints, leading to improved performance on 1944 and 45 aircraft designs.
It won't win them the war. But if managed correctly could lead to overall greater US casualties.