Fixing this stuff is related to knowledge about damage system which is in RWM tweaked/hacked somehow. Barbarossa is no longer active and there is nobody else who knowns how it works. For example you can kill Nashorn crew with grenades but only if it's turned from behind.Flamethrowers - they seem to kill everyone inside the tank immediately witch is unrealistic
mortars should kill tank crew of the M18 nashorn wespe hummel and SU76 easier because they have no roof
I'm not sure, indestructible infantry in buildings is part of original game. Just whole army shooting 5 minutes into 1 building and can't kill anything.. It never worked well although modders have tried to eliminate it for years. In case of trenches it's endless story.I believe that in sudden strike 2 houses were balanced perfectly
The rest of things are more or less related to game engine.