It definitely isn't and whilst you haven't addressed any of my points, I've shown it's not that simple, particularly not in 4E.You're making this way more complicated than it needs to be. If you want the PCs to die from the fall, then they die. If you don't, they don't and take a lot of falling damage instead. It's really just that easy.
Yeah, and that's going to make it EVEN MORE relevant as to how far the PCs actually fall! There's a huge difference between Featherfalling 500 feet and the party having to go down a few hundred feet to meet up with you (or vice-versa) and Featherfalling 5000 feet and it likely taking you at least 10x as long to meet up.I'll add, if you're clear with your players that "Hey, you're going to be really far up, if you fall you'll die," you're players will prepare for this by prepping feather fall, tying ropes to each other, etc.
If you DM fiat killing a PC from unspecified falling damage in 4E (given how difficult it is to die in 4E), the players would be in the right to say "Okay, you're not the DM anymore, roll a character", frankly. That's just a more individualized take on "rocks fall, everyone dies!". Be even worse in 5E, where barring optional rules falling can at most knock you to 0 HP and thus start you on the Death Saves.