Kanan, Lumi, and Qui-Gon are the ones you'll want to replace. Kanan is solid, but is generally better used with Phoenix. Qui-Gon and Lumi are good early on, but later on in the game they'll be pretty close to dead weight, especially Lumi.
Fortunately, Grandmaster Yoda's event is probably the easiest legendary, so you should be able to at least unlock him whenever he shows up next.
If you're able to access Jolee Bindo's node, he's an essential Jedi to have as well, as he's a ridiculously tanky healer that can revive (with his zeta).
Longer-term, sinking any Guild Event currency you get from Territory Battle/War (you're in a guild, right?) into Hermit Yoda is also well worth the lengthy farm. Bonus, he works on lots of non-Jedi squads too.