Unix was probably a great IDE by the standards of 1975, because literally every design decision about Unix was made based on the criterion of convenience for a 1970s programmer. Those decisions haven't aged well: fork() sucks, lack of completion-based async I/O sucks, ill-thought-out file, socket, and process APIs riddled with TOCTOU bugs suck, two-letter YAFIYGI commands suck, untyped pipes suck, and don't get me st…
Of those, only
> two-letter YAFIYGI commands suck, untyped pipes suck
sound like problems with unix as an IDE; most of what the article discusses is unaffected by underlying APIs.
I also feel like I should question whether you're not attacking a strawman; modern unix-likes are continuations of unix, but they're not stuck in the 70s. For example, AIUI everyone agrees that fork() has shortcomings... which is why we have vfork (and I think others?) now.