Why would it? Panthers could fire back and destroy it, doubtful with T-34s versus a JT. And why would a 100mm be allowed to do super damage while 75mm/L70 wouldn´t be?
Thing is: Its role is redundant if you think about it. Su-85s couldn´t go through heavier armor, yet they do ingame. Why a Su-100 then? Fix the units that are ingame. The biggest sin imo is that the T-34/85 isn´t available outside a doctrine, while it really should be the standard spam tank.
Because it is a game and it needs its tanks to be balanced...and SU-85 is already horrible compared to Jadgpanzer 4 which outclasses it in every aspect...
Oh and for your "realism" argument,check this:
"The SU-100 arrived in operational units in October 1944 and immediately became popular with Russian crews. It was able to defeat almost every German tank on the battlefield, only to be outmatched in 1945 by the King Tiger".