I think the difference is that the mentor might introduce them to the magical world, but its still up to the character what they want to do with it e.g. to quote the matrix "But I can only show you the door. You're the one that has to walk through it." And the decision as to what to do with it has consequences and changes them.

Or to use another example - gandalf might mentor frodo, but yet it always seems like frodo's accomplishments are his own and gandalf didn't really do all that much for him when all is said and done. Frodo is a hero and an interesting character, but i wouldn't want to be him.

Anyways i don't think the problem is lack of life lessons (even if they are lacking) its static characters and lack of stakes. Characters that were born ready are boring to watch. We like watching characters that change and adapt to circumstances whose choices are meaningful and consequential. The protagonist who was basically born with super powers, does not face a challenge and doesn't have to adapt their personality, is a boring character.