Have you played a good chun? I can only think of 2 or 3 high level players that use her, in the world, so for most people the answer to that question is no.
She has good damage, the best instant overhead in the game tied with Wolverine, except she can combo off of hers, a special move that's invincible from startup to frame 11 and is ~+9 on block, and generally decent tools.
She suffers against zoning, but to say she "ain't shit" if you have a decent projectile is nonsense. She's mid tier, for sure.
The effort and technique it takes to play her at her version of high level will just get you better results with a different character.
From the general FGC populace, a lot of people think Chun is terrible because they only people they see USE chun, are terrible players that don't know any better. The only point at which Chun becomes a threat... when you can stop dropping her combos to start doing good damage, and start using her more advanced techniques, is also the point at which players start using primarily Top 10 characters.