Combining some buttons into one

[Seraphor]

If you want to know what spamming the same button for your entire DPS combo feels like, go ask the healers.

This is problematic for branching combo's, because you need to know what place in the combo you are currently at, in order to keep mental track of your buffs, debuffs and gauge accumulation.
By having it all on one button, you are forced to watch your hotbars continuously, and can no longer rely on muscle memory.

Also, there are some jobs it simply wouldn't work for, such as Monk, whose Perfect Balance opens up all combo moves to be used in any order you like.
Ninja would go down from 4 to 2. So that only saves you 2 buttons, but you want to know what part of the combo you're in for Bunshin/TA windows.
Samurai would still require at least 3 different buttons for it's combos, so it's not saving much space.
Dragoon could theoretically go down from 8 to 4. But again, as you will want to weave Life Surge in before True Thrust, this will make it much more difficult to keep track of.
Dancer will at most shave off 1 button in it's basic 1-2 combo, as the rest are procs that you can hold.
Bard doesn't need this at all.
Machinist... might actually be a job this could work for. You don't ideally weave anything in before Clean Shot as you want to use those on Drill/Anchor instead, and the basic 1-2-3 combo doesn't give you anything besides continuous gauge, the only hurdle here is keeping track of that 10 battery gauge from Clean Shot. But this may still result in the job being 'too simple'.
This sort of 'simplified gameplay' will go hand in hand with 'simplified jobs' and people don't want their jobs being simplified anymore. It's not merely a QoL change.

There is a place for this however, GNB has it in Continuation, and I'd be all for another new job that features this mechanic, if it worked for that job.
But if you apply it to existing jobs, you'll get as much backlash as the healers are giving right now.