Probably the core of the issue here is that VMS and derivatives tried to hard to fit everything into a generic handle/fd interface while UNIX historically came

Probably the core of the issue here is that VMS and derivatives tried to hard to fit everything into a generic handle/fd interface while UNIX historically came with a smaller core with many important API surfaces (like signals or timers) only relatively recently getting absorbed under the unified handle/fd interface, giving the impression it's an afterthought. It's also not something that works on all Unices (e.g. afaik macos has no timerfd). But in all fairness, that problem only exists because OS speciation, as it's biological counterpart, is not as clear cut a concept as one would desire.