How true! In my 30 years in the industry, I haven't experienced a single PM who was a net-positive (though I've heard that some are awesome), and some that simply made no positive contribution whatsoever.
I had one program manager who was awesome, even though we certainly didn't need a program manager (~40 person startup) per se. But she realized what was going on and then kept the PM (and everyone else) off my back so I could get the job done.
First and AFAIK only time in that company's history that a software project was delivered on-time.
Of course, after we shipped, it was all "congrats, but now you must do things properly like the rest of the company".
Not sure whether that's "sigh" or "LOL" or ¯\_(ツ)_/¯