In tournaments? If its the case, then its most likely due to top players during tournaments rarely pick soviets, most of the time they pick UKF\USF.
I didnt see relic post win-rates for automatch anyway. Not like, I'm saying soviets arent weakest allied faction, not over-all weakest, but I would like to see win rates.
You can compare pick rate of factions between pre patch and post patch. Most of the players are the same and we have completely shifted from going SU/USF and OKW to USF/UKF and OH mostly. The distribution for allies faction is not as bad though as before (no one picking UKF) while Axis has arguable shifted more towards OH.
As far as automatch stats, we have Syphon thread. It's only for 1v1.
https://www.coh2.org/topic/105597/1v1-automatch-stats/page/1#post_id822826