It's also not clear whether the overmatch spot on the turret actually has gone IMO from those pictures as they seem to have highlighted a weird area but hopefully it has.
The IS7 still has the better turret, the extra degree of depression and of course the alpha.
I have also always thought the 260 felt much taller with a much more easily hit lower plate compared to the IS7. It also has 300 more HP as well so clearly the IS7 survivability is a lot higher than the 260 even with these changes.
Those turret armour changes are more quality of life than anything, they just remove the annoying 'wtf!' moments after some bob auto-aims you and then pens your gun mantlet because reasons. I seriously doubt aside the lower plate the vast majority of players know the weakspots on the 260 but most owners do because they suffer those annoying pens.
It'll still retain the cupola and the shot trap will still be there as well for those who know how to fight one.
Even if it is slightly better than an IS7 or 277 (which is doubtful IMO) is it really an issue? It's a reward tank, that you barely see, you get for free, accessible to anyone and you have to slug a through a load of painful missions to get. It being slightly better (and I put emphasis on slightly Mr T22) seems fair enough for a reward tank IMO.
Can't see it being OP in the current meta, it's still just another flavour of an IS7, 277, 113, and 5A, and I also doubt it'll challenge the all round good at everything, is it a heavy, is it a medium, no it's f8cking soviet power creep that is the 430U.
As for the T-55A it was always worse than the T-54, as when it first came out it had minor gun advantages but a much worse hull and worse mobility, then they buffed the T-54's turret and it became even worse.
Currently the T-55A has a worse armour than the Type 59, the T-55A has 200mm frontal turret compared to the Type's 230, has a worse cupola (though only one) and doesn't have the turret ring weakspot.
This change brings it up pretty much to the same point it was to the T-54 before, similar turret, worse hull, similar mobility, slightly better gun.
Just wish they had given it better pen, would have taken a 230-240 AP round over the mobility buff. At least it should be playable though.