Invasion is making the game less fun

Losing to someone with much lower combat power feels like a bug, and since it's not getting fixed, the game is becoming less fun. Starting from Diamond rank, I wonder if they're using hacks, but most players' HP refills quickly even when it's depleted... With the lifesteal stats shown, it shouldn't refill that fast, so it feels like a bug. Until it gets fixed, I can't play Invasion, so I'll just run through Tombs, Towers, and Raids and then quit.