There are many types of sexual behavior in that trope, from the 'slutty cheerleader' to the 'pure and innocent flower'. Siwon is the 'reluctant heroine': a heroine who wants to be left alone, but everyone keeps coming for her despite her being completely ordinary. But due to her absolutely awful stubbornness and idiocy, she refuses a perfectly easy solution for her problems bc she 'doesn't want to get involved in trouble'. Meanwhile trouble just keeps on snowballing bc she won't fucking take the obvious easy way out.
Tldr: Siwon is the stupid love child of the worst characteristics of Bella Swan and Clary Fairchild.
(Don't get me wrong, they have redeeming points. Siwon just didn't inherit them).
Siwon is worse than every 'dumb girl in action movie' trope put together.