I believe the tier 8 su-101 is in need of a buff, specifically its gun.
175 pen and 250 damage stock on a tier 8 TD isnt great.
After about 60+ thousand XP, it finally gets a decent gun. Its stats are 219 pen and 320 damage.
I suggest either buffing the stock pen to around 190 or making the level 4 100mm D-54S gun its stock gun.