I didn't say that those who do rewrites are clueless. I said that rewrites are really hard - far harder than most people expect.

That weird switch behavior? I almost guarantee that someone, somwhere, some when depended on that behavior. Either they no longer use the switch behavior or they no longer use the tool, or they just don't use the rewritten version. But how do you know that? In the best case, the code would have a comment: "This code is to simulate Berkeley 3 behavior for users porting from..." But even that doesn't tell you whether anybody today still depends on it.

I mean, it could be a valid strategy to not rewrite weird behaviors - any of them - and see what breaks, and then only add the ones that are still needed. The upside is a much cleaner rewrite, with fewer (and, hopefully, better documented) weird behaviors. The downside is that you have to break stuff temporarily to find out. (Hopefully you break it in live staging rather than in production...)