Button bloat can be easily solved by combining multiple combo abilities into a single button. Take Dragoon for example:
Combine "True Thrust", "Vorpal Thrust", "Full Thrust", and "Fang and Claw" into a single button
Combine "Disembowel", "Chaos Thrust" and "Wheeling Thrust" into a single button.
There, now we have 5 slots we can put to better use. Gunbreaker (And PVP actions) already have the action that does this (Gnashing Fang -> Savage Claw -> Wicked Talon), why not do the same for all other actions? Button bloat isn't a good excuse for removing Hissatsu: Kaiten.
It doesn't necessary make the game easily, combos already have glowing outline indicting the next viable actions.