I can say with confidence that is almost entirely due to light vehicles.this
Faction winrates even follow the tier of light vehicle strats, lol
1. t-70
2. m20 -> stuart
3. Luchs/Puma
4. 222
5. AEC
Oh look it's the same order as the faction winrates.
You see it play out this way because light vehicles are the first unit that can single handily win a match. When you have the best players in the world playing against each other they are all incredibly skilled light vehicle drivers, whomever wins the light vehicle duel that happens in 80% of the matches will win the game. The T-70 especially tips the scales into the Soviets favor significantly.
You don't see these win rates in normal matches with average players because they can't handle the light vehicles as well. A skilled player with an unmatched light vehicle can absolutely trash their opponent. The solution is to revisit light vehicles again to try and make them strong without being able to single handily win a match. I recommend reducing raw power and adding more utility to keep them as high skill units, without being able to wipe the opponents entire army after one mistake.
I wouldn't even say Soviets are that much better than the other factions, it's pretty much entirely the T-70.
But dont worry now they will buff evrything that axis have thanks to people like incendiary rounds because guys like him thinks Wermacht is weak because brumbar or elefant lol but that statement is false.
For example Mechanized was popular because WC truck no because mighty sherman76