You seem to have had a very successful PhD experience. You write approvingly of your advisor, acknowledge the ways in which the program benefited you, and have respect for peer-reviewed literature.
That being said, I'm not sure that your experiences are typical. HN regularly has commenters and posters that have been disappointed by their forays in academia. One recent example was posted only two days ago:
I imagine that a good PhD program is, by definition, likely to be beneficial. Probably above "independent learning" by leagues. However, it's worth considering what an average-case or worst-case PhD program looks like. Those may not compare as favorably to "independent learning".
Having talked to many PhDs, candidates, and students from other schools at conferences, I'd say that my experience is typical, at least for quantitative fields like math/stats/CS/engineering. Most of the horror stories that get thrown around the internet are from a vocal minority. You're far more likely to speak up if you had a bad experience and feel strongly about it. And it's not always the student's fault, but there are a lot of people that choose to do a PhD and drop out because they weren't a good fit. It's hard to tell the difference between a bad fit and a toxic program when you only hear one side of the story and can't ask their peers if they are exaggerating things to make themselves sound good.
Most PhD programs are small, and most advisors aren't famous academics. They are generally good people, but there are a few wackos (that's why it's important to have a few conversations before picking an advisor). The "typical" PhD is probably glad to be done, but isn't chomping at the bit for a second one. Nearly all will admit to stress during the program- with qualifying exams, comprehensive exams, and proposing/writing/defending a dissertation, you're bound to feel stress.
The jokes about being a "grad slave" are pretty common, but an advisor delaying a student's graduation because of the cheap labor is much less common. People claiming to be a grad slave to cover up their slow pace are probably more common. If a student actually has a strong case that a professor won't let them defend, then the word usually gets out and that professor will have a hard time finding more students (more reasons to have lots of conversations before choosing and advisor and committee).
And I definitely don't think that the peer review process is perfect, but it is more rigorous than publishing a blog post about something you learned. Not publishing isn't a deal breaker, but it's evidence of doing something. I trust the research skills of an M.S. that has a couple peer reviewed articles published more than an M.S. that has claimed to have done a self study program but has nothing to show for it.
The other link is about "philosophy PhD". This seems to be the big difference -- when I talk to non-CS PhD students, they often seem to have much harder time and worse conditions that CS ones.
My theory is because of all the opportunities. At least in CS, there is no problem in finding the job with "incomplete phd", and such jobs usually have a much higher salary than PhD stipend. This means that if you don't like PhD, you just leave -- and income increase associated with such action makes it really simple.
From what I understand, this is not the case for non-CS PhD specialties.
That being said, I'm not sure that your experiences are typical. HN regularly has commenters and posters that have been disappointed by their forays in academia. One recent example was posted only two days ago:
https://news.ycombinator.com/item?id=21740833
I imagine that a good PhD program is, by definition, likely to be beneficial. Probably above "independent learning" by leagues. However, it's worth considering what an average-case or worst-case PhD program looks like. Those may not compare as favorably to "independent learning".