Bear in mind it can depend what country someone is from.

Traditionally, a Briton saying “I’m kind of okay at this” might mean they’re one of the best in the world (mustn’t blow one’s own trumpet).

A Briton who says “I’m great at this” (or anything beyond “pretty good”) is likely an arrogant charlatan.

In contrast, an American might say “I’m good at this” to mean “I am better than average”.

I’d imagine other countries have their own tendencies for under/overstatement.