Controller has access to far more than 16. You gain an extra 16 slots from the Expanded cross hotbar, and you can access yet another 16 if you make use of W Cross Hotbar.
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No it makes you have to switch between sets which is annoying to do. So there is no reason for mirage dive to be on a separate button when you want to hit it right after the jump anyway. Dragoon has way more then 16 skills making you switch between sets. So more buttons that change to the next part would be optimal.