For Marauder at least, you will need to use around 5-7 skills for your single target primary rotation depending on spec.
Then there are also a lot of other situational skills which you may only use once per combat or from time to time, but nonetheless important and should have keybinds (e.g. Charge, Disruption, AoE etc).
There is a lot of abilities, and nearly all of them are useful. Currently I'm binding 1 2 3 4, Q, E, R, F, X, C, V, T plus an entire set of those keys + modifier. Although only a few of those skills make up my primary rotation, all of those skills are frequently as situation changes.
Those two bars only have my combat abilities. Non-combat abilities like mount, lightsaber stance, buff or out of combat heal are on side bars. Nonetheless some of those are bound anyway.