You also have monks which have a different comboing mechanic. They use stance buffs which enables the use of skills and aren't sequentially locked like the other melees.

Though one way they can tone down on button bloating is get rid of skills that add no depth to the job. Things like stone 2/3, gauss round and dwad. Or at least redo them so it's not a waste of a slot for most of he time, like ninja poison, turrets and most of mch skills that share cooldowns for the same purpose in different areas.