You can talk all the technical details and try to confuse that point all you want. But I disagree with some of your points and you are attempting to confuse the real point. You are trying to compare average citizens to a SWAT team. You have introduced "headshot to a hostage taker" which I don't see where you got that from because if it a hostage taker, teachers would of course wait until police arrive instead of taking actions themselves.
Technically I own a Bushmaster Model XM15-E2S.
Before purchasing my pistol, I looked at various makes/models/calibers and grip options. Sub compacts I can only grip with 2 fingers instead of 3 and the trigger falls on pad between the second and third joint of my trigger finger. The most comfortable sub-compact to date has been a .40 Baratta sub-compact. Of non-sub compacts, I looked at many different manufactures and in .40, .45, and 10 mm. In each and every case, the trigger would naturally end up somewhere on the third joint of my trigger finger, regardless of grips used. And in many cases my pinky finger would only be partially, not fully on the grip. I knew the DE fit naturally and comfortably without any modification, so although I wanted a 10 mm or a .40, I went back to .44. I simply got tired of searching and having to mod other handguns when an un-modded one would do just fine and I never found a suitable combination of gun/grip mods.
How "handy" it is depends entirely on the individual.