That would come close to doubling the thickness and weight of the phone.

I’m sure some people would buy a 16mm thick, 400g phone but I doubt it’s the majority.

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.