why does just cutthroat have to be so much harder than 4 feat.

me and my friend have learned the new dungeon this week and thought we might grind for the title. we took down first 4 feats no problem. doing challenges and cutthroat by themselves, challenges took a little longer due to slight complications, but cutthroat took us 5 phases on harrow, and with a third on contraverse for final, my friend on well finality auger and double rocket pulse and me running the same but with cuirass t crash, 3 phases was half the bosses health. i don’t know what we’re doing wrong but the health pool is massively overturned. any tips?