Is there some real smutty shoujo webtoon with a good plot and art style-

"it looks like i've fallen into the world of a reverse harem game. "
It's Not a shoujo to begin if it has smut scene it's not a shoujo.

I think you're searching in the wrong genre. Try Josei + webtoon (josei tend to has good plots)

http://www.mangago.me/genre/Josei,Webtoons/?f=1&o=1&sortby=comment_count&e=

Or Smut + webtoon. (smut tends to be written often by male author... I mean you can destined they're pep with a male harem king).
http://www.mangago.me/genre/Smut,Webtoons/?f=1&o=1&e=Yaoi

Typo: *you can tell they are with a male harem king protag*

Bless u TvT

;) I hope you find something that interest you!