Interesting. I skipped from an iPhone 6 to an 11 Pro, and when I pick up my old 6 now it is both so thin and light as to feel very fragile, whereas the 11 Pro has a dense, hefty, solid feel in comparison. I have briefly used someone else's iPhone 12 and it didn't feel any different from my 11 Pro, to me. YMMV and all that.

They're easier to drop, but I haven't found mine to be excessively fragile. My iPhone 8 Plus is four-years old and has been dropped many times. It has few chips off the corners but is otherwise going strong.

Just because of the rounded edges that made it slippery?