Doom should work fine, if you don’t have him rip
Just parry and dash back, when the tenacity is on cooldown parry heavy. I soloed it everytime, try to heavy counter his sp1. The path is easy, just stay away from the opponent till they are at like 15 regen things and start parry heavying with mags. The boss may be annoying for you but MM and some heavies work well will omega, bring sabertooth instead of venom for the synergy. Parry heavy with mags also works but its a long fight.
U dont need doom for that fights there are youtube videos on ppl soloing that fight with a 2* rhino...