Being able to gear-swap is not about efficiency. You don't need to make it so your character is amazing at whatever it can have gear for at all times. Does this enhance your character's performance? Yes. Is it necessary? No.

Efficiency is about how effectively you perform your role within the rules and limitations of the game. Removing certain limitations does not increase your personal efficiency. It increases the things you have to do to be efficient. Sure, besides that fact that it sounds like a wet-dream for any elitist as it adds more to do to be considered good, it may sound engaging to hear that you have more to do to be effective... however that's also where the problem lies. In order to meet this new requirement of efficiency, you have to prepare multiple gear-sets for each job/class and write elaborate macros. I'm sorry, but when I think of efficient gameplay in endgame content, I don't think of spending my time making elaborate gear-swap macros after gathering pieces of gear that I carry around for only 1 WS/Spell.

Now all of that was the technical argument against gear-swapping. Then there's the obvious, simple notion that even in a Fantasy environment, repeatedly blinking/changing your shirt and pants during a heated engagement is just absolutely ludicrous.