Combining some buttons into one

[Seraphor]

Theoretically you could do it yourself (combining the skill in one button) via macro... although, it will add some macro clunkiness here and there...

I'm not sure how, because in all cases except Monk, all combo skills are on the GCD and can all be used when the GCD has completed.
If you macro combo skills 1, 2 and 3 to one button, then whatever skill is first in the list, is the skill that macro will use. You'll just be spamming 1 over and over.
And of course as I state above, Monk is the one job this unequivocally cannot work for.