Having tried OpenBSD 6.7 and 5.9 (the latter just to try the compat layer) I can tell you you're not missing much. I also tried the compat layer in FreeBSD, which I'm pretty sure is based on similar code due to how you use it.
This thread is interesting for me, as I'm coming from the other side as the OP: I use OpenBSD and wonder if NetBSD is worth a try. I'm happy with a minimal OS, so I'm unlikely to switch to something with more features than I really need, but I tried FreeBSD first and I've mostly written it off for now. Though I did get farther with the FreeBSD compat layer.
Now for my experience with Linux compat: Originally tried it on FreeBSD, got PyPy running (that was my main goal, since the native PyPy on FreeBSD is deprecated, perhaps until the upstream devs figure out how to bootstrap compilation) but getting simple Linux apps to run in X was a matter of library issues. I got each dep copied over one at at time, until it complained about glibc. So FreeBSD, I only got working with command line apps.
When I enabled compat in OpenBSD 5.9, the last OpenBSD to feature the layer, it wanted me to install something in /emul/linux that I was unable to find (few mirrors feature the 5.9 tree that I could find). I guessed that the /compat/linux tree in FreeBSD (these are Linux ELFs, not BSD binaries) might correspond to /emul/linux (which didn't even exist, except in documentation) on OpenBSD, so I made an archive of it, copied it to OpenBSD and unzipped it to /emul/linux.
At this point I could tell that the compat layer was working, because instead of complaining about the wrong syntax (in a binary) it would complain about a missing lib instead. I would copy the lib, then it would complain about a different dependency. And so on, but unlike with FreeBSD I never got a single Linux binary application to actually run. What they removed wasn't much. As for Bluetooth... I don't use it in GNU/Linux so I don't need it in BSD, but I can imagine a number of people with hardware that is useless without it.