Personally i like to go by my thumb reach on my MMO mouse.
The Razor Naga, and most MMO mouse 12 side buttons are really awkwardly positioned and they never seen to fix that.
Without removing my hand from a good position i can hit 1-6,
As such i like to be able to play a class on 6 buttons per bar.
1-6
Shift 1-6
CTRL 1-6
(ALT causes too many game breaking problems since it has so many Windows/background program hotkeys that can mess things up.
q
e
r
(Also the shift and CTRL versions of above)
Mouse wheel click (And its Shift+CTRL options)
If i cant fit things within that button range then i feel things are far too bloated.
FFXIV both does and doesn't fit depending on Job BUT that's not the main problem/bloat issue with XIV> the problem is it has many buttons/ability's that do the same thing, Dancer for example, how many ability's that "Hit all enemies in front of the dancer doing 50% less damage per enemy hit, requires proc to cast" does one class need? (Dancer has 3. They are all the same ability by a different name.)