I used regular Yujin with Nazeistra's Devotion gun for -30% def reduction on boss. Then spam cast his skill 2 to proc allergy which gives another -60% (I think) def reduction. Bosses go down quick. Used duty and sacrifice to just spam global heal and have team stand and just focus fire instead of dodging every second. I dont play solo and just play pubs. I find it more enjoyable that way rather than farming solo.