140mm APFSDS next to 120mm one. medium and light tanks days are numbered.
There is a limit to how much you can push even with ERA. Heavy MBT are the only one surviving tank on tank battle or anything in future. So the notion that tank weight need to be kept low in 50 tonne range is just pure fantasy. Even armata is 55 tonne with ammo and will require armour upgrade to it's gun turret, increasing weight further up.