Its not going to win against a panther, but it won't be a complete pushover like an M4 is what I mean. It will pen reasonably frequently which means it's got a chance, especially on the move.
So what you are saying is that it loses, just less badly. And see, that's the problem, Ez8 doesn't really "get" you anything, it stil needs AT support against a Panther, or anything bigger just like a regular Sherman, so you still need a Jackson anyway (or enough AT guns/Zooks to cover its absence)
But unlike a regular Sherman, it doesn't secure you a solid AI advantage on the field
And, as has been said already M4A3 + M36> 2 x M4A3E8 (maths, yo)
And it'll stay that way, since any time there's a situation where generalist spam wins with specialists, a nerfbat comes around to say hello (spamming one unit to win is not-kocher around here)
I mean you can use a doctrine slot, and 140 fuel to get a tank that lets you win against P4, and Stug maybe (compared to regular M4A3) and loses its AI punch, adn you're discouraged to build more than 1 anyway.
Or you can get adoctrine witch gives you a hero unit (M26), and good inf.
Or you can get a doctrine which gives you a rocket artillery, and good inf
Or you can get a doctrine which gives you Self propelled howitzers, and M1919s (as in, good inf.)
Or you can get a doctrine which gives you awesome AI tank, and cheap AT vehicle (Armored)
etc. (and good assault inf)
Even M4A3(76) is better, that at least has some serious DPS, so it's better for flanking.