Calm down y'all

It's not a bug, if it were they'd no doubt be able to fix or change it to be a different way if they wanted to. They were able to patch out the solo leveling thing where you quickly change classes, so I don't think they consider having someone outside your party kill stuff to get you exp a bug.

Edit: Also yeah, with it you can level blu to max in like under 2 hours. Why would you want to spend money to skip such a small grind? Besides, you'll still have to unlock all your spells the normal way.