Tbh, the m20 is fine, maybe give it armored skirts straight off the bat and reduce mp cost a lil bit for better timing. but even then i find its pretty decent. Just comes down to how well you can micro it.
The only value it has is desperation comeback when you got like no other options at all. The t70 is just a straight up better option and is essentially on a level where youd have to make the su76 insane to even give it a remote chance of competing with it
Hetzer+mp40s are in a really good spot right now, i'd say maybe making hetzer 10 less fuel but no more than that, or making the mg upgrade come with it wihtout requiring muni, but eh, not neccessary.