Russians are not that much faster except for some anomalies like the IS-7 and the T54 but have high damage guns and the best armor structure in the game(except for the cardboard mantlets on their high tier tanks). Their downside is that they suck a lot more when not upgraded.
Germans are more accurate but less damaging and what they lack in intelligent armor design they make up for with having more of it then anyone else. The very steep dropoff of AP effectiveness, the spotting bugs and the general scale of the game all nullify these advantages, leading to the forums thinking the russians are overpowered.
Americans have slightly worse guns, ungodly turret armor but styrofoam hulls. They are good at camping, which, due all the bugs mentioned above along with the scoring, repair costs, map layout and objectives is by far the dominant tactic in the game, and everybody utterly despises them for it. And since people test their stats by a 1v1 dogfight on the field of campinovka, they are also seen as woefully underpowered. On top of that, they suffer from not having their full tech tree yet and most of their mid tier is missing the highest gun upgrade.
Worth noting that the most fun tier(2-3) has the best tanks being a german TD, a german premium tank and an american artillery sharing it with a russian artillery that's a tier higher.
And stay in tier 2-3. The quintuple xp days gave everybody at least reasonably close to tier 8 their top tanks so the moment you step out of the newb bracket, you will be relentlessly matched against fully pimped vehicles of the highest theoretical tier you could fight. I ended up selling my KV and KV3 on account of facing an IS-4 every single match and am having trouble on my IS 1 through 4 tanks doing anything due to 8 now being bottom tier and an unupgraded 9 being no match against the upgraded ones.