But this isn't simplifying gameplay, this is removing an extremely outdated way of controlling your character. Just think of how much easier it would be in terms of accessibility for those with disabilities even...

The fact of the matter is that this would be a massive upgrade to the current system. There is absolutely no point in having, for dragoons for example, 8 different buttons when it could be turned into two. That is just an unnecessary hurdle in terms of control design.

And if that would make you forget where you are in your rotation... Well, you could just quickly glance at your one single icon for the combo to know which one you are at...

It is much better to focus on designing hard encounters that is hard because of mechanics, not because the players have an unnecessary amount of buttons to keep track of. That is old school thinking.