There's various ways around this (like capping amount of experience per level by source), but ain't game design fun?

It depends. Personally I think they should make alternatives more easy. For instance, under Options, for people to pick other ways to level up. Does not have to be 1000000 ways, just, say 3-5 ways in total, first one being the main default and only the main default is kept balanced, the rest can be unbalanced, just allowed per option as-is.