I think we'd need to see some sales figures for cases. The case I use on my 13 Pro (casetify) adds enough size that the bump is barely an issue -- there is maybe a 1mm edge around the actual camera bump. It's very nearly the ideal. I don't know how common this size case is, though -- common enough that a mainstream case company sells it, I guess.

I'll concede the point on the weight, although I bet it'd be more like 350g.

I doubt Apple would add drop-friendly materials in such an expansion of the phone so most people would be putting a case on top of the iPhone Brick, making it even thicker and heavier.