speaking for myself, as of the light-saber quest on my sage, even with a companion, I needed to be at least 2 lvls higher . For instance, say I got the light-saber quest at lvl. 10 I actually waited until lvl 12. I couldn't solo it before that time.
The question you pose is one of those types that do not have an answer that is true across-the-board because not everyone is necessarily as skilled as someone else even if they are the same lvl, similarly equipped etc.
So, even though sage is my favorite, I have to grind a bit more than most to go through solo, your mileage may vary