The devs nerf some players to get them to spend more money.
Notice how I used the same hero lineup as the two recent clearances, and my heroes are at a higher level with higher power and better equipments and relics. I am often stuck at levels where players with lower level heroes clear.
Also, on a separate note, customer support for this game is abysmal. They will blame you when the game doesn't work properly, and half the time they don't even answer your question. They have problem with basic English comprehension.
