Leia could help Luke get some of his effects off if his levels are high enough, but the leader skill isn't super impressive otherwise. If her basic is upgraded enough, she gives everyone critical chance up anyway, so it's kind of redundant.
At that level, I think STHan is decent. However, if Vader and Sidious are showing up in your arena already and you are facing a lot of debuffing teams, Luke might actually be useful at that level.
At this level, you should be already forming a plan for a synergy team moving forward. Have you made use of the resources on the forum in that regard?