I'd like auto combo buttons for the abilities that REQUIRE a previous combo action to perform the skill, simply because it would help free up space on my hotbar and make it so my fingers don't have to keep breakdancing awkwardly when I need to position for mechanics and execute said combo at the same time. I'm talking things like the GNB Gnashing Fang combo which takes up three spaces on your hotbar when it may as well take up just one (until 6.0 at least, thanks Endwalker), or DRG Fang and Claw & Wheeling Thrust which you ONLY press in order after executing a combo.

For the normal combo abilities, I'd just leave them alone. Things like Perfect Balance/Formless Fist and Meikyo Shisui give you a reason to use abilities outside of the conventional combo. I know that SAM is a bit... hotbar heavy, but as it's not as highly dependant on hitting positionals except on finishers it's not so much of an issue to me.