No, solo RPGs are designed around levelling. MMOs not so much because you need some sort of plateau where people can actually play together. Imagine how hard it would be to play with your friends if there was no level cap and end game content. WoW being top heavy is not a problem, it's a design choice.
As far as levelling being "a core part of the content" it's really not. It's more of a mechanic just like the gearing system to prevent insane amounts of class stacking and flavour of the month rerolls.