I'm just gonna rant here, if you want to add on go ahead.
Whenever there's those things that are like "_ are attacking _" I always go help with it because I get pretty good rewards, and then I just leave the boss at the end for someone else. But several times I have accidentally joined in only to hit the boss, which eats through all of my supplies before I die. But this time I was like pffft I just bought a bunch of stuff, I'll beat it easy. I had spent all of my badges on strong elixirs, I had bought twelve revival droughts, plus a bunch of random things I had gotten as a reward. But the boss was SO OPed that I used ALL of those and still died! Every time I was close he would just recover!
And I'm sorry but I just needed to get that out. Perhaps I'm doing something wrong?

I took a glance at your team and I think you have at least some gear issues going on. Not sure about proficiencies. If you want, you can message me regarding what proficiency trees your pets are in and who the tank is and I can see if I can help.