I would say that the Maus and E-100 could go to 7.3.
The biggest problem is that the Maus has an overpressure bug going on right now - and its internals are extremely easy to overpressure (and kill in one hit). The E-100 doesn’t have this issue currently.
The IS-3 could certainly go to 6.7. Its turret rotation is horrendous and the gun reload and gun depression adds to the horrible feel, certainly.
The IS-4M going to 7.0 is also fair IMO. Quite insane that it’s 7.7 currently.
Ferdinand/Elefant could certainly go to 6.3, and were 6.3.
The 268, however - I would say is superior to the Ferdinand due to its higher mobility, relatively better gun, and better armor. Along with the very useful 14.5mm. 6.7 is more fitting.
The Ho-Ris are better than you give them credit for, though. I’d reckon the Prototype could be 6.3 and the Production 7.0. They’re quite nimble overall and their armor is very strong.
The M6A2E1 does have very good stats and the gun is quite good, it’s also not very slow - so 6.0 is a bit of a stretch IMO. 6.3 is quite fine. The T26E5 is also one of the best 6.7s in the game, so I wouldn’t say 6.3 is right. The E5 is extremely strong.
The IS-2 (regular) is fine at 5.7. It was 5.7 for a long time, I played it at 5.7. And it was good. Not OP. Just good. About right. Wouldn’t say 5.3.
The 1944 to 5.7, though - definitely not. It’s not a fantastic vehicle but the armor’s considerably stronger and I’d reckon 6.3 was on the edge of “usable” - REALLY don’t know why it went to 6.7 when the Tiger 2H is considerably better, especially the premium one.
T95 at 6.7 makes perfect sense. No qualms there.
The Tortoise is quite bad, yes. I would say not quite 5.7-6.0, though. 6.3 would be absolutely perfect and would go along with the beautiful existing 6.3 lineup.
Black Prince at 5.3, especially with the reverse buff - I’d reckon is a bit too low. It is extremely slow, however. I would say 5.7 would be fine, though. 6.0 perhaps to be sure.
I would also add the T-10M, which really shouldn’t be 8.3. The IS-7 is the same BR and considerably better, and vehicles such as the Chinese Type 59 and Type 69 at 8.0 are honestly better. And a couple others.