Nope, not true at all. Not even remotely.
Every single MMO available right now, and even the old ones like EverQuest, allows for multiple ways of levelling your character other than world questing. This just tells me you haven’t really spent a long time playing other MMOs.
The only environment where what you’re saying is true is in single-player RPGs and even then there’s variation depending on the type of RPG. A game like Skyrim or Oblivion? Which are fantastic RPGs, allows you to level whichever way you see fit, without even touching the story once you get past the tutorial.