Well - the basis of the grounds you place your conviction onto, are quite questionable to me.
Everyone has his own reasons/reasoning's - and if an opinion or differentiating opinion is forwarded in a civilized manner, I got absolutely no problem with that.
So we simply agree to disagree in regards to that "contribution" matter and Stalin's factual agendas and actions. Same would apply towards FDR. I am not well informed in regards to his "achievements" towards internal USA issues.
But in Contra to a Winston Churchill, FDR only got decisively involved in WW2 - due to Imperial Japan, Fascist Italy and Nazi-Germany having declared war onto the USA.
Factually the US was simply foremost interested in tapping into those "new and stabilized" economies.
Before the war declarations onto the USA, he and the US government couldn't care less about Stalinist, Nazi or Fascist dictatorship and it's repressive policy - and neither about those 20+million dead Chinese civilians.
The latter applies to all Western powers or countries. And it is important to be aware of that, in order to understand today's China's position and view's towards the West.
Are you aware that whilst Mao was fighting the Japanese since 1937, the ROC only declared war onto Imperial Japan, Nazi-Germany and Fascist Italy on 9th December 1941.?
The ROC clearly only reacted in conjunction with the USA - meaning loads of $$ coming into someones pockets. And the Check's were signed by FDR. It is also no secret that the majority of military actions by the ROC were directed towards Mao and not the Japanese.
FDR was clearly aware that the USA will defeat Imperial Japan - and that as such a power vacuum (a future huge market) would arise in China. And he simply based his bet solely onto the ROC, just as Truman did - which proved to be a very false perception.
As I stated before - it's simply and always only about the money the USA can make - aka achieving global economic domination. And during or the time before WW2 it was Nazi-Germany, other Fascist countries and Imperial Japan that were threatening or opposing US global economic dominance. The moment WW2 in Europe had ended - Stalin took over the geographic and economic vacuum and started his crusade against US dominance.
Now - a revived but economically still weak Russia since 2000 and a still emerging power called China took over from a dissolved Soviet-Union to halt and oppose US dominance.
Just as the Ukraine conflict was additionally incited by the USA and it's supporters within the EU - the same goes now for Taiwan.
There are however major differences between Taiwan and Ukraine.
Ukraine was and still is a poverty stricken country and it's population was made to, or simply believes that being a NATO and EU member is going to make them all rich.
Taiwan is already rich - it's economic well-being however is in majority controlled by China. (exactly what the USA simply can't abide) There is no hatred between Mainland and Taiwanese Chinese. There is actually a general acceptance between the two. (aside from some students and "inspired" followers who demonstrate at times for democracy and LGBTQ rights).
In contra to the Ukraine population the vast majority on Taiwan is simply not willing to risk their good livelihood for an independence attempt that would automatically mean war - since China logically can't tolerate US military right in front of it's mainland. So the US government (no matter which one) is simply inciting a presently ruling Taiwanese party that holds less then 35% support amongst it's population. The comedian on the other hand at the time of the government change held AFAIK around 70%+. and the Ukraine is a fully recognized sovereign state - which Taiwan is not. Not even officially recognized by the USA.
That overall, American views and perceptions of the same occurrences/issues, vary quite a bit from those beheld by e.g. Europeans and Asians is fully granted.