Supreme Leader Kylo Ren is the best GL

I disagree and think he's the worst GL I have right now. I have every current GL except LV, and SLKR is the one I use the least and when I do am often disappointed. Yes he was easy enough to farm, especially now since his requirements are very minimal in terms of kyros. But I find that any time I use him he's often the lone survivor of the battle, which is not ideal in certain game modes like TW or GAC where you lose out on banners because of it. Saying he "doesn't need another specific character in the team" followed by "if he only had a conquest character...so he could be meta again" seems to contradict the first statement. 

I do agree that he needs a lifter, which would certainly help his usefulness. I've been saying that for a long time how FO has essentially been left alone since SLKR released, while Resistance has had several lifters (Zorii, Ben Solo - even though he's not Resistance). My thoughts would be to include Praetorian Guards, Snoke, or General Pryde. They could even add Commander Pyre from the Resistance cartoon. 

I have all GL except from Jabba and Ahsoka Tano. I mean he doesn't need another charachter to work well, I use him in all factions of the game and works perfect. But right now in arena he is not meta because of what you say, he is normally the only survivor and the FO faction is not that strong. In GAC I use him to defeat OP Rey for example, it's a problem he is the only survivor, but finishes the battle. In BT normally he is also the only survivor, but does all the waves. 

Totally agree with the lifter, even a Kingths of Ren (although in the movie they were trash, in the comics they are interesting) could do the job.

I hear he works well against Jabba, but for me it's a 50-50 win rate. I often use Starkiller against Rey in GAC, with high success rates.