The sad fact is that even with GK, Jedi just arent competitive in Arena right now. Before CLS was released i was running zQGJ lead, GK, GM Yoda, JKA and zzR2. You can replace GK with OB and R2 with Aayla Secura/Ezra but your going to have a tough time moving up.
Frankly, as a faction Jedi just arent very useful right now for much of anything. Thier effectiveness is limited in higher level TW and even with a maxed squad, Jedi can only get you through a Combat Mission in day three or four of Territory Battles.
Some individual Jedi such as Bariss, GK and Ezra are still useful, but as a faction they desperately need some attention from the devs to help make them viable.
I would suggest choosing another faction/squad composition if your looking to progress in arena.