Ok so going back to game modes. Either way in any game mode regardless USF ALWAYS has to manage more units and use more Micro. Do you see the point yet where your arguement is about to break down?
IF USF can do OK in 1v1 and still have to manage that many units regardless then WHY are you saying they lose more in 4v4? See where the Logic fails there? USF regardless of game mode always micros more. Except they lose more in certain game modes....starting to see the breakdown yet?
They lose more because the amount of micro they need to succeed in supporting and working with their team mate increases. In 1's you can handle a single player easily because you have more than enough stock units/counters to that 1 specific faction. But beyond that things get complicated.
A well coordinated Allies team can easily ruin a Axis team, IS2's backed up by Jacksons is the deadliest synergy combo out there. But again, this requires a plan and good micro which isn't very common against the average player.
Can you see the logic here Higher game mode ---> More coordination and micro required ---> Harder to play. It has nothing to do with specific units being OP or UP, rather, it has everything to do with Soviets, USF and OKW being all super cheesy factions.
How can a OKW player micro and coordinate medium tanks and support weapons that don't exist. If the entirety of OKW was adjusted to were it required about as much micro as USF did, then you would find far less players playing OKW in 3's and 4's.
If you want an example of a very very good unit nobody uses because of the micro needed for it, here it is: