And nothing that statistically make the Ez8 a great tank let him compete with the panther making it as poorly efficient as the T34-85 on the AT department on anything above the Pz4. I really don't know what so complicated to understand here.
The T34-85 is a great tank because while naturally outclassing Pz4s it has great anti infantry impact and good survivability.
There are 3 ways to make the Ez8 useful. Or a T34-85 clone but the segment is already filled with the sherman dozer or a panther clone with obviously the cost increased accordingly. Third way would be to make the doctrine so good people would pick it regularly and build the Ez8 because its in it.
Your issue then seems to be that you want much more out of the E8 than it's supposed to give. There are an extremely limited number of tanks that can go toe to toe with the Panther. That is by design.
The E8 is not and will not ever be one of those tanks in part because you can hop out and heal the fucking thing anywhere even if you don't have a lick of infantry. This is significant and the drawback for this is that usf tanks are not meant to be panthers. The E8s job is to make the enemy NEED panthers. You can bitch and moan about it not beating a Panther and not having the AI to be a t34/85 but here's the thing: the Panther doesn't either, but yours comes out sooner to do what it can in the meantime and they CAN'T build p4s to make up the difference because they will get clubbed like nobody's business.
ALSO there are options beyond the limited ones you propose, ones that arnt shit. The E8 doesn't need changes, the doctrine does. It doesn't need to be made OP so everyone picks it and builds E8s (seriously sit for a second and think of how beyond trash of a suggestion this is. It's a codguy level suggestion) we've already addressed the shit tier idea of making it into a Panther further up (another ill conceived, unthought out suggestion that shows a clear disregard for actually trying to achieve balance)
Seriously awful suggestions that show a clear misunderstanding of the faction, the unit, unit roles, interaction between factions and general common sense of even the lowest fathomable sort.