OpenBSD may be the last one to go. Though right now, it has a big browser issue. No LibreWolf on it anymore ( https://librewolf.net/installation/openbsd/ ), and that is the only browser other than Tor that doesn't let the entire web know everything about your system, by default. It's pretty silly to use OpenBSD but then also use fucking Firefox. Or even the webengine or webkit browsers, those don't actively spy on you like Firefox does, but don't hide your information either.

Anyway, the way that the directories are structured is very unimportant (and it sucks on every OS, though Windows does it the worse, it's blatantly structure to hide things from the user). Haiku is probably the most viable OS that is not Unix-based. It runs a decent number of programs, including Emacs, and it comes with bash and all the basic core utils, so it's still a lot like Unix. Unfortunately, because it could be less shit, but also fortunately because it could be even more shit. The window manager is kinda like PekWM in the sense that you can draw a window to another and have both of them in one frame, like tabs. You can also glue them together.