Could you fix the endgame bosses in coop?

Hello,

I've been playing a lot of coop with my friend and it's getting a bit annoying. I tried Waystone Tier 2 solo and killed a boss in 30 seconds. When I play with my friend, we have to fight for 10 minutes, etc. But if we do Sekhemas and Temple of Chaos the bosses die faster like in the main acts. I don't understand what is the reason for punishing coop players in the endgame this way? I hope you fix it!