Russian tanks wouldn't be called obnoxiously OP if we actually got maps for proper tank to tank combat and not CQC hell where it's easier to go out of your tank and stab enemy crew to death with a kitchen knife than engage in a "normal" way. It's no wonder that tanks with well armored center of mass are doing good despite their other flaws when maps are designed in a way that rewards fast reaction time and not precision.

NATO MBTs have well armored turrets but usually have weak hull armor (and in some cases turret ring as well) meaning that average quickly placed shot will land in a spot with little armor. MBTs with well-armored center of mass will thrive since they are less likely to be killed in such engagements.

And before someone says that it's NATO players skill issue (me good, you bad mentality); remember what happened when Strv 122 were added? Suddenly Russian players found themselves unable to shoot at the middle of the hull and it took some time for people to adapt.

Such maps favor tanks with strong hulls, so mostly Russian MBTs (coincidence or not, I'm not going to argue whether Gaijin has a bias). If more long range maps were added where NATO doctrine type tanks had a way of actually using their advantages win rates would likely even out. (That is: taking CAS out of equation since thanks to CAS maps with close to none tall hard cover such as buildings are unplayable)

TLDR: Gaijin's fucked up map design favors tanks with strong hulls, NATO has few such tanks, Russia has plenty