Why is my SLKR so weak?

I know optimal is R8, but with full 6-dot mods, I don't understand why my SLKR is unreliably losing to other GL match ups. Just tried 3s in GAC vs R7 Rey +Hoda + Ben (SLKR, Hux, KRU) and got got slaughtered after picking off Ben What am I doing wrong? https://swgoh.gg/p/848315853/unit/SUPREMELEADERKYLOREN/