(TD meaning the su-85, jp4, jackson, and the Firefly. I am not including the atg)
weapon accuracy against a target is calculated as the listed accuracy multiple by the target's size.
For example, the 75mm kwk 40 have a accuracy of .025-.05, while the t34/76 have an size of 22. Therefore the kwk 40 have an accuracy of .55 against the t34/76.
(in practice it is actually higher due to stray shot, but .55 is a decent baseline).
Heavy tanks (and more powerful units in general) have a higher size. The tiger for example have a size of 26 compared to the pz4's 22.
This is actually historical and realistic as thicker and heavier armor require more complex suspension, and more powerful gun are generally bigger. This in turn also demanded more powerful engine, which are generally bigger as well. The tiger was 3 meters high compared to the p4's height of 2.68m.
This means that heavy tanks like the tiger are easier to hit, but in theory make up for that fact by having higher HP and armor.
The issue with Tank destroyer right now is the fact their accuracy is too high.
assuming the target have a size of 22 (panzer4).
the jp4/FF 0.04 - 0.06 = 0.88 - 1.32
the Su-85 .04 - .055 = .88 - 1.21
the m36 .035-.05 = .77 - 1.1
this completely nullify the advantages of having a smaller target size. Even with the 50% accuracy penalty, a moving td still achieve an accuracy of 44% against medium tank.
TD doesn't need their current insane accuracy to counter heavy tank, as heavy tank are easier target to hit.
Assuming a target of 26 (tiger and king tiger).
panzer4 .025-.05 = .65 - 1.3
panther .03-.06 = .78 - 1.56
this means the extreme accuracy on the TD are complete overkill. Their accuracy could go down to .025-.05 and still be good against heavy. the Su-76 currently have an accuracy of .025-.05
(atg are different since they are support weapon. I've left out the stug since it's only got 50m range)
