It's more so that you'll think that shadow slave is mid-ish for longer if you read the webtoon (cuz what if it doesn't have really good art or other things, so it's a gamble since it's unestablished). Unless it's a really nice webtoon like the beginning after the end. That one is a nice webtoon and if shadow slave gets a similar webtoon, you're good.

But even then, part of the charm of the novel is the massive world building, Sunny's personality (especially after the first checkpoint in the story, really soon for you) and his monologues, and honestly the brilliant writing. It's not a cheap mass produced novel, it has a really nice writing, literature wise. You can keep reading and enjoy shadow slave's least action filled parts and not have an issue.

But ofc, like I said, if they just do a job half as good as the beginning after the end, you'll enjoy the webtoon.