I was having the same issue. I switched to arc bow with exploding heads and overload, barrier scout and anarchy. Storm caller with surge detonators mod. Got though it many times with ease. The massive arc burn made my grenades, super and anarchy melt.
Id stun the overload with arrow or made them lob 2 or 3 anarchy and watch him melt. Same with barrier when stunned, lob a couple anarchy.
At the boss I’d save as many anarchy rounds as I could. Spam the boss with it pop stormtracer and melt. Run and grab the chest.
Storm trance is useless against the overload champions, and I don’t have Anarchy.
My point is that the champions pare overturned to the point that it’s making the game one-dimensional (everyone is having to run the same loadouts) and the mechanics breakdown if you’re underleveled.
Understandable.
The mobs and yellow bars are tough, but manageable. It’s the overloads where the situation breaks down unless you’re apparently running Anarchy or Lament.
Which is a serious design/tuning problem.