how can i write my protagonist as accomplishing stuff without them turning into a sue?
Didn’t I just cover this?
It’s entirely reasonable for your character to be skilled. It’s entirely reasonable for your character to have past achievements. The only question is, “does it meshes with their history and focus?”
The problem with the Mary Sue label is that it’s over applied to female characters, and drastically under applied to male characters. This means there’s a lot of people who don’t understand the term. They’re sure that being a Sue is a bad thing, but all they understand is it’s pejorative for characters they don’t like, and a label to cry about when it’s attached to a character they like.
I’ve provided multiple definitions, many times, but the very short version is that a Sue is an uninteresting character who trivializes the rest of the story they appear in. The result is that the character overpowers the work as a whole. You don’t get a compelling story. You don’t get anything else of interest. All you have is this single character, and they tend to be fairly boring.
Okay, so, here’s the problem, most Sues (male or female) are going to be overpowered. When you don’t have a concrete grasp of what a Sue is, it’s easy to mistake any powerful character for a Sue, and just apply that label whenever you dislike a character, while arguing that characters you do like couldn’t be Sues.
What this means for you is, if your character is interesting, and doesn’t overwhelm the story, they can be powerful without becoming a Sue. Like I said, I’ve gone into far more depth on this in the past.
Something else I’ve said before, and I’ll repeat it for those in the back, misogynists are always going to label your powerful female character as a Sue. It doesn’t matter how well written they are, whether they fit their world, whether they’re actually overpowered, or just powerful enough to participate in the story. They’ll attack, and there was nothing you could have done to avoid it.
Do not be afraid to write powerful characters. Be careful, but not afraid. Someone will lob the term, “Mary Sue,” around because invoking a fifty year old parody fanfiction might hurt your feelings. As critique, it’s mostly meaningless.
If something in your writing doesn’t work, don’t be afraid, work on it, and fix it. But don’t give up the dream because somewhere a “well akshully” neckbeard feels threatened.
The only important thing to remember, when writing any character: Your loyalty is to the story not the characters. The story you’re telling is what matters, there’s no value in making things easy on your characters. The harsher their trials; the sweeter their tribulations.
You will always have people who dislike your work. That’s life. If they can articulate things that don’t work for them, you might see weaknesses in your work that you can improve. Don’t take criticism as a personal failure, look at it as an opportunity to improve. If a critique doesn’t tell you anything, it’s not useful and you can junk it. “Your character is a Mary Sue,” without any further discussion is not useful.
How can your character be powerful without being a Sue? Tell a good story with compelling characters.