"Consider that the Glock can take tremendous impact and still survive. (As in a thousands-of-feet fall at terminal velocity.)"
Okay, your pistol will survive the fall, but you won't. You'll just be a puddle on the landscape. So what's the point?
Or maybe you dropped your Glock out of a plane. Lot of good that'll do you if you need it and good luck finding it. So what's the point?
You know, Ruger salesmen used to toss the Speed/Security/Service-Six revolvers around ranges and even drive over them and they kept working. It's not like Glock invented durable guns.
Re: "tenifer-finished slide"
Actually, Tennifer is a metal treatment and not a finish coating. They treat the metal and then the slide is coated with something else.
FN uses Melonite, a similar salt nitriding process. My black FNP-45's slide is Melonite treated stainless that then receives a black coating.
External vs. internal parts? I refer you the 1911 and Browning HP. Both models have seen many more decades of serious use than any Glock and managed quite nicely by all accounts.
So, sales of the FNP-45 appear to be on a real roll now. The primary reason seems to me to be that folks appreciate the safety in addition to the decocker vs. the previous decocker-only. Be that as it may, I'd be happy with mine if it was the only one ever made. I was buying a pistol, not joining a club.
John