It's not just the author's personality that makes a Mary Sue or Marty Stu. And it's difficult to not write insertion or surrogate. So I would beg to differ in that few authors don't have insertion; they just don't draw attention to them and turn them into the obnoxious person who knows all and does all. Those that are aware of them might try not to insert into a main character; but until they are skilled, that awareness and effort can often take away from the organic nature of the character.
If you have an ubermensch character no matter how much you try to avoid this label; it becomes difficult to not have readers identify it with an insertion and then a Mary Sue .
There certainly are a large number of those types of characters in today's fiction.
More often than not it seem when we identify such things and give them names, we automatically frame it as something bad-denotes poor writing or lazy writing-and this type of critique often seems to become a cliche of tropes and begins to lose it's power. Just as a writer should be careful about how they use insertion and surrogacy the critic should be careful about what they are identifying as such.
