It is not a trope about competition, it is a trope about a fighting style, which can be used in a competition.
It's not a fighting style. Wing Chun is a fighting style. Karate is a fighting style. Those are practiced movesets and skills. This is specifically
about fighting in any manner that confuses an opponent. Hell, even the example you just gave me
isn't about a fighting style, but what steps someone take to win a competition. The trope is about a character who competes with another character by confusing them. It's a competition trope.
I still also think Skill Gate Character goes in the "imbalance" section because this is about Competitive Balance, which exists mainly at the highest level play.
Just two friends playing the game because they like it is competitive play. X-Box Live versus is competitive play. A game being competitive doesn't mean it's only about the highest level