Your team idea is solid. I am trying to synergize with Phasma, to get more attacks, stuns, counters and assists. But the only way to really do it is to "let go of the security blanket" and drop Lumi, and it's just very hard to do.
I will have Kylo at 7* tomorrow and it seems a shame not to use him. Like Asajj, a very versatile character.
If anyone should go from this team, ironically it should be Phasma. But she's just too good to drop. I will probably experiment with both Kylo and Lumi in the 5th spot and see how it goes. If Asajj retains her group heal, that will make things easier (on offense anyway, on defense she'll be useless.)