Even in wow a quest based game lvling off monsters is still faster some of the first people to get lvl 90 in MoP got it off grinding mobs. Just because yoshi said standing in one spot killing mobs for no reason all day is not the best does not mean its not effective. Devs can never be 100% sure whats effective or not, even if they intended it a certain way (NIN XI). In ARR you can still grind mobs do quest do leves and have fun lvling in dungeons, that's plenty of options. One thing i love about he Xi purist the funniest thing about that game was lvling solo was the fastest XP if your job could do it.