KRU Zeta too powerful

I was almost in the same boat as you - just use basic abilities once he gets stunned by daka or av. Avoid inflicting debuffs unless it's more plague, and for the love of God don't let him heal above 100% or you'll have to rinse and repeat.

Kru is very beatable, you just need to pay attention to his kit so you don’t get caught off guard. NS and OR are probably like the worst 2 teams to take on FO since they apply a ludicrous amount of debuffs. If you use the right team, though, it’s easy. FOO is the only cleanser, so once you kill him just apply healing immunity/shock to KRU and he goes down pretty quickly. I used very undergeared seps to beat my opponent’s KRU (Dooku lead) on my last match. G7 magnaguard and G11 Grievous kept the Kylos (G12) stunlocked until KRU ran out of protection, then unresistable healing immunity kicked in for 2 turns, which was more than enough time to take him down. You just need to use the right tools, that’s all.