I think you will win allot damage from getting your rings and earring to 21-22stars honestly haha , i think your missing out on 50-60att per 17-21/22 star you do not have at this point ( afcourse not talking about arcane, cause thats a pain to get to 22 ) and this boss is such a pain in the ass i general, my friend nightwalker lvl 281 , 22 star everything besides arcane gear. Dies out 50% of the time rng D: i am super impressed how you survived this long with 5 lives xd
I don't think any class is weak in general and even so there's more factors like support, survivability, etc. Lumi has really good survivability and I'm missing a lot of stuff from my gear and IA, so it's not necessarily the class that looks weak