Too many characters are broken - what is going on with EXP?

I dont understand how some characters are so overwhelming OP compared to other classes - trying to play with someone who is a high level monk is just boring to be around and usually they charge in take some damage and laugh it off without any real challenge, same for the warrior. Its hard to have fun with groups if they're just doing a rambo. They need to be seriously debuffed in what damage they can do compared to other characters.

What is going on with EXP? I can be the same level as a friend, completing the same tasks with the same lvl enemies but somehow im on 10mil less exp. I know why its because their class is broken and OP killing enemies before anyone else gets the opportunity. It makes playing other characters less appealing cause why would you want to be stuck doing nothing going nowhere.