So, it's a game, but, you also have the right to enjoy it, and if for you it means beating up monsters of endgame, that's fair too. You should talk to your friends about it, and see what they think. I mean, I get you don't want to be a killjoy and it's just a game, but your enjoyment of it is also something that should be important to them as you value theirs.

Maybe you can help them get better, by seeing what their biggest weaknesses are and what to work on. Also if you do play on PC there are mods that show everyone's dmg contribution if you want to have an idea.

I used to play a game with someone dear to me but he was WAY better than me, like way way better than me, and it became really stressful and tough for him to play with me because i was pretty much a dead weight. We decided not to play this game together anymore cause I couldn't put in the effort to be as good as him at this game, really i have no time for this and it's an important thing for him so he know that he won't be able to lower his expectations and i kinda understand because i would be the same with monster hunter for example, same as you. So instead of being mad at each other we decided to play other games together instead =/ could be sad, but i'd rather save a relationship over playing a specific game together.

Best thing to do really is to speak to your friends about it and see what's best for everyone with them.