If he was an actual Gary Stu, there wouldn't be an infirmary where you are sent to every story event. About everyone kissing his ass, let's see: Xavier is like that with every young mutant as his role of older kind mentor, Rogue does kiss his ass because he is the only person she can actually interact with, Laura straight up kicks his ass for most of the first season and only starts coming around near the end, Jean is a neurotic with a desire for anyone to like her that tries to win over the one guy who doesn't have a negative impression of her, Storm is legit just being nice.
Challenges like getting his ass handed to him by Juggernaut and Sentinels? Or what kind of challenges are you thinking of?
No, it would not be fun.
Maybe because the game is very early in development and they decided to focus on the girls first and then start introducing the rest of the team? Content with Kurt is coming and Colossus is gonna be bro-able in chapter 2, maybe even starting a friendship at the end of the first summer, Scott and Logan are referenced many times and will probably come with Colossus, shit Logan even has a line of dialogue.
Maybe because this is an introduction to the world so the story is just starting? My sibling in Christ, the game is in a very pretty alpha, patience is the name of the game.