`ed` was developed in 1969. That's a remarkably uncharitable take, considering `ed` itself and its derivatives (like `sed`) are still useful today.

This is accurate in the same way as saying "a rock chiseled into a wheel with a stick as an axle is still useful today". Or maybe "a mechanical calculator and a book of logarithms is still useful today".

Sure, it still exists and still does what it used to do, and its derivatives surround us. But nobody does that any more because nearly everything else is so superior, it'd be ridiculous to do so, except as an art piece or when you literally have no alternative.

That's not a fair analogy at all.

sed is basically the stream interface for ed and it's one of the most common unix text utilities, and even ed has its uses today. I remember using it on a machine I was remotely connected to. For some reason the terminal output was garbled and neither vi nor emacs would render properly, but ed worked fine. Obviously you wouldn't use it day to day, and yeah, you wouldn't use if you have any alternative at all, either. But the fact that it still has some form of (admittedly very limited) competitive advantage over modern tools makes it useful to have /bin/ed handy, even if you actually use it once in a blue moon.

No more uncharitable than saying that modern developers suck at their jobs because they can't make Sublime Text in the same time as it took Ken Thompson to make ed.

That's not the point of the article, not even remotely.