You can keep complaining all you want, it's a good measure, it works, it's gonna stay. And lmfao you're completely wrong, most if not all MMOs do have something like this in place. If they don't hard cap your level, you don't gain any experience from lower leveled enemies, PRECISELY to prevent you from overleveling in one area killing chumps and then steamrolling the rest of the storyline.
What does WoW being a subscription game have to do with them also doing this I absolutely not get at all. How does that make a difference?