(b) a small fraction of kids branching off into fringe networks that are off the radar and will take them to very dark places very quickly.

This already happens, and I don't see how a law like this would significantly change the volume of edgelords and incels funneling into imageboards

There's internet culture precedent for this. 4chan itself has an early history of picking up leftovers from communities that were banned on other sites/forums/platforms.

4chan's origin itself fits that archetype, as well. It was created when a hentai subforum got banned on a larger forum, and the community moved over to the new imageboard.

It acts as sponge for more than just edgelords.