The logic is precisely BACKWARDS.
Grip a traditionally stocked rifle. Drop it down to waist height. Your wrist can remain at a fairly comfortable angle and still keep a firm grip on the wrist of the stock because it is close to horizontal, the way your hand naturally wants to hang by your side.
Now, do the same thing with an AR-15. That vertical grip is now quite uncomfortable to hang onto because you have to twist your firing hand so severely forward to keep a grip on the weapon.
Now, logic like this is utterly lost on gun ban folks who usually don't know or care to know anything whatsoever about firearms.
WHY human-firearms ergonomic development has favored pistol-gripped weapons is pretty simple.
Face a target with nothing in your hands. "Put up your dukes" like you're going to punch the target. Hands are now up at chest or shoulder height and they will be roughly in the perfect orientation to grip an approximately vertical grip.
While many of us grew up with more traditionally stocked rifles and shotguns and are more comfortable with them at this point, that is a learned thing, not a natural thing. The way you must roll your wrist forward and down to grip a conventional stock's wrist is a lot less intuitive and natural than a more vertical "pistol" type grip.
That's why so many modern weapons -- especially precision rifles and also fast-action military style rifles, and heck, my kids' Savage Cub .22! -- come with a more-or-less vertically oriented grip. It is, from a human body/ergonomic perspective, just BETTER.