The western front doesnt exist in a vacuum. Without doing anything in the east, there are very few ways to improve Germany's position in Western Europe. Making the pressure in the east simply weaker for whatever reason strengthenes the German position in the west, not to mention removing eastern...
Lets assume that for whatever reason, either better Axis performance, poorer Soviet performance or dumb luck, the Germans manage to take and hold the targeted Leningrad-Moscow-Rostov line during Barbarossa.
What do the Soviets do next?
Not really that different from what Guderian envisioned in the early 30's. The 100 tonner with 150mm gun is maybe a pipe dream, but with no Versailles restrictions and with more industry and resources these ideas could win out.
If you insist.
If the Americans aren't coming, Michael looks nothing like OTL. Maybe wiking's "Peace offensives" idea goes through, and instead of Michael you have a series of Spring-Summer offensives that finally make the Entente call for peace.
Standard CP victory, Germany gets...
The issue with this type of thinking is that the victorious powers IOTL didn't stop armour development. France had more tanks than Germany did during Fall Gelb, they just failed to use then properly.
And besides, the two countries you mentioned, the USA and UK, have the luxury of large bodies...
And why would it be so much different in the latter case? The hulking WWI-era rhomboids are an evolutionary dead end, and people back then weren't stupid. They wouldn't just keep designing A7V type monstrosities in perpetuity.
But if its really so important, no US entry in 1917. and the Entente...
Question: how do you think that Germany's tank evolution would go in a Central Powers victory TL? Would Guderian's guidelines be followed? Would the tanks that came out look similar to their OTL counterparts?
The "USSR would have won regardless" is an internet meme not supported by actual historians specialised in the Eastern Front. America's involvement was decisive. Perhaps not militarily, but economically it was invaluable.
On a side note if I ever were given the task of re-designing the Leman Russ, I can't think of a better base for the design than the ARL 44. Something about it just captures that faux WWI aestethic Imperium war machines excell at.