Getting one-shot by Mercenaries as CWS Chieftain

PoB: https://pobb.in/s7rkM0pJ2m8s

I get to 100lvl easily by doing breach + ultimatum and only died like 2 times 98 to 100. Wanted to try some merc + boss rush but at every 5 maps or so I'm getting one-shot by mercs. I tried to skip the merc I'm dying but I don't know if I'm dying to specific merc because I'm running Trarthan Scarab of Infamy and I might be dying to side mercs. Any help is appreciated.