Problem with Turing the E8 into a Panther is you will STILL have a Jackson along side it. So then you have a durable meatshields that can punch at heavy cats AND a 60 range powerhouse that can outrage, brawl and chase. It's no contest between being in the shit or outside of it shooting in with no risk of return fire. That's the problem with the E8. It's got no purpose because the Jackson makes it obsolete.
There is no scenario where USF Sherman variants work while the Jackson is the perfect AT machine in every single scenario.
The only way the E8 could find a nich is as a command vehicle with extra abilities that make its unneeded role irrelevant. Sorta like the command panzer where the tank itself is next to useless but the abilities it brings have value.
This isn't all that different from having a jp4 and Panther. Cost is similar except Jackson has a turret. I don't think its an issue.
The problem is not Jackson is an AT machine. Its that the E8 sucks to use because it sucks at everything including cost.
There are some 'bad' tanks to use but are made better because of a niche role. Take Churchill for example, the only thing its good for is tanking damage and being a relatively cheap damage sponge. M10 is a worse-off Jackson but its a really cost effective AT vehicle with a speed boost ability. 221 comes stupid early like UC and has a late game resource boost.
What does the E8 have going for it?
What is the E8 good at? Pretty much nothing. It gets out classed by the other stock options. Its expensive as heck so deep flanking manoeuvres (where the tank shines) are punished easily. It doesn't have cheap cost, it doesn't have good AT, it doesn't have good AI, its armour and HP is mediocre. What does it have going for it? Pretty much nothing. The Commander upgrade is a nice experimental change but I don't think its going to save it.
IMO its pretty sad to see such an iconic tank be out of use and be so bad to use.