It doesn't surprise me terribly that, in the sizable userbase, some people manage to make it segfault - particularly running unknown plugins &c. The first example you give is even found to be a bug in a compiled external extension. I've not read through any of the others...
I've been using vim pretty much daily, across many versions, over roughly two decades, and I literally do not recall encountering a segfault. I would be hugely surprised if "segfaults all the time" is a more typical experience for an individual user.
For good ideas for async stuff you should try emacs. You don't have to keep using it, just look at what it does with its built-in asynchronous subprocess handling. The interactive python shell is particularly neat, but it also has grep and compile functionality that doesn't block the editor as it runs, and a gdb mode that (based on my very brief go with it) seemed to work pretty well.
One neat thing I use it for is TTY capture from a target system (usually games console or embedded device) over a serial or network cable. Run your terminal program in emacs at the start of the day, and emacs will dutifully capture all the terminal output as you work. Search, save and manipulate TTY output using all the commands you know and love.
Well - except for `.'. Or `*'. emacs doesn't do those two...
My experience certainly doesn't make that implausible. I am pretty careful about async IO in terms of how my software interfaces with me, and this translates to less uncontrolled use of it generally.
I've been using vim pretty much daily, across many versions, over roughly two decades, and I literally do not recall encountering a segfault. I would be hugely surprised if "segfaults all the time" is a more typical experience for an individual user.