I think that the term "Mary Sue" needs a better diffinition.

The standards set for a character to be considered a Mary Sue fit most main characters in a canon story anyway.

Case in point: Twilight Sparkle.

Favorite student to her world's leader.

Incredibly powerful beyond what anyone has ever seen before dipsite being young and untrained.

Being well-liked despite being so socially awkward she doesn't even want to make friends in the first place.

Magical girl!pony episode one.

I do not consider her to be a Mary Sue, but do you see my point?