Every gun loads, though, and it gets in the way from dancing around the ship going from gun to gun like a prancing fairy battle-hardened machine of death. Scrambling around the deck amplifies that feeling that everything is in this state of controlled chaos, the heart of the game's fun.
Let me put it this way; as it is right now, an engineer can repair something or buff his own gun during reloads, given a bit of skill. A gunner, on the other hand, can at best shoot two Hwachas on a Galleon because those are two closely-placed heavy weapons with the longest reload in the game. An engineer can already run off to do repairs during reloads so long he gets back in his seat in time, a gunner suffers a penalty for switching to a different gun (which would normally give him a big incentive to bring more than one ammo even if the guns themselves only benefit from one type) as outside a Hwacha Galleon it's impossible to keep two guns loaded with special ammo at once while firing them.
Everyone is going to be able to leave a gun, yes, but the gunner will have an overall great effect with his guns versus the gungineer who can't make use of the new tactics with just his single ammo type. As for regular engineers, they'll be dealing with the effects of those improved gunners.