Not that I have seen, I have read 4-5 different threads about this and NONE of them give a valid reason why AA is a bad idea
I am not really surprised that someone biased towards implementing AA would not find any "valid" reasons for not implementing it. I can't really change that, either.

there is only so many actions you can preform in a given unit of time
And you know what's so good about this? This game isn't even close to hitting that limit of the number of actions and even if they speed up the combat even further, it won't happen. I can list dozens of games out of my head that have you perform double as many actions as in this game, as well as making you move around and let you "talk" at the same time. Your definition of "involving" is also flawed. Special skills aren't nearly as important as basic attacks in this game, and neither is moving around in the battlefield. Neither of these 'issues' has anything to do with the stamina gauge or the lack of auto-attack, and both issues can be fixed regardless of if auto-attack exists or not. Auto-attack won't fix those issues either, it will only make it even more obvious that the current combat is flawed and broken.