This is a great introduction to the OpenBSD-specific syscalls, and an awesome list of resources. Makes me want to write more C.
Writing code using just OS’s native libraries (usually C-libraries) is definitely a model, I think that will get more popular, given OS-centric focus on security, multi node distributed computing (distributed memory and file systems).
Which is why, I think that the languages that offer safer programming models, yet can rely completely on the OS-provided libraries (rather than leveraging their own stdlibs) – will get more traction.
Obviously, there is C for that. But, additionally, the two languages I know of that do that is Better-C (a subset of D), and, I believe, Zig.
I do not think, that at least Better-C is yet available on openBSD, however the work to port it appears to be a beginner task ( https://wiki.dlang.org/LDC_project_ideas )
What about when the standard library for a language can use those syscalls under the hood? I think that’s a reasonable compromise for writing good higher level code.