I see three possibilities to improve this, 2 nerfs, and one (interface) improvement:
-1- Disallow customizing.
I considered quick swap is a sort of "buff" to basic weapons. e.g., to give you a reason to keep a RL once you got the missile launcher (which is, imo, insanely imbalanced. especially once nanomachic xD). In fact, I see it as the same reason why you can't rocketjump with a missile launcher : a simple nerf, for an exceptionnal weapon.
-2- Allow a number of quick-swappable weapons (e.g. 10), but not EVERY weapon to be instantly accessible at the same time...
I think this is annoying to implement, since the list would have to be specific for every game, and would have to be customised/saved... bah, annoying to use, I guess.
-3- Just make every swap instant, without having to bother with those BS quick keys
Btw, if this isn't considered an overpowered skill, this sounds like the obvious way to improve it. I rarely picked up this skill, but something tells me it's probably one of the most insanes you can get... even more than my beloved Fin3.
Anyway, I know I can play without it, it's what I do most of the time, but I ***HATE*** losing efficiency just because of a lousy interface, and that's why this particular point really bugs me.