It's a filler move that procs other (better) abilities for TK, nothing more, nothing less. You can use it outside of TK spec, but its usually better to use something else. Now that's not isolated to Sages, that applies to a lot of classes. TkT is only situationally useful for non-tank Shadows and Rupture is primarily for Annihilation Maras while Vanguards will rarely use Full Auto.
This is correct, you can't arbitrary compare different skill of different classes and different spec without looking into how the actual skill functions in a particular place. So let's just entertain your example of Disturbance and Charge Burst. The two class specs that find them viable is Telekinetic Sage and Sharpshooter Gunslinger respectively. This is what they do for each class.
Disturbance give you: Force regen buff, instant cast TK Wave proc, chance to proc additional attack for 30% of the damage, power up all your force attacks up to 3%.
Charge Burst gives you: a chance to use Trick Shot and procs Quick Aim buff.
Disturbance will look inferior on paper at the beginning, but if you put them in practice, a fully powered up Sage's Disturbance will equal if not surpass a Gunslinger's Charge Burst.