Yes, that is the exact problem. For the cost of 1 ISU, I do and will always get 2 su-85s. Nobody uses isu-152 for any AT because it RNG bounces even p4. With 8+ seconds reload, it takes as long as a Firefly but fails to reliably penetrate and do damage. And, it's not good at everything because it has like a 16 second ammo switch. By the time the switch is complete, it should already be flanked and/or dead.
The AI is also RNG. Sure it's great if it hits but with it's accuracy and projectile terrain pathing, it sometimes also hits nothing at all. that's 8 seconds plus another 8 seconds to reload and fire again. All this time, it may hit nothing for a 720 MP 260 fuel unit. IS-2 performs better and all heavies have had their MP cost reduced to around 600 for Tiger, IS2, Pershing. This one stands out as an RNG unit like B4 which is why usage is so-so and definitely never used as an AT weapon.
And dude, your playercard barely shows you as playing SOV.
Lulz, tell me, how many 1v1 or 2v2 as SU have you played? Since these are most competitive and give best sight how units perform.
It's not even close to being RNG machine. For AI ISU is the best unit in game. Tell, which unit is better and I will prove you are wrong.
As for the bounces from P4, there is 15% to bounce from vet 2 Pz4 or from OKW Pz4. So I would not whine that 70 range unit has 15% chance to bounce from 234 armor unit.
Funny how you call almost 750 random (+ plenty AT) as Soviets "barely" xD