X mm phone + Y mm case < (X + 1) mm phone + Y mm case

X+Y+1~=X+Y when X,Y>>1. Does it really matter if you have a 16mm or 17mm phone + case?

Thicker, stronger phone = not need protective case.

Cases protect against scratches and dents, not breaking the phone in half...

They are not that fragile if you don't drop hard. Never used case for A50, it still looks almost new after years of active use. But for iphone I got a thin case, to protect popping out cameras and to make it look cool. Main concern is thieves if I travel somewhere, not the physical damage.

Unless you drop them very hard, cases are not needed anymore. Been using a Iphone 12 pro max for 4 years without a case, I don't even look twice and I drop it from the table.