Yeah, it's complicated.
"A friend" (cough) had an exploitative advisor. But this friend also learned a tremendous amount doing all the gruntwork, writing the code, writing the papers. Yes, "my friend" did take over six years to graduate, but "my friend" was pushed harder than he'd ever been pushed in his life and probably harder than he'll ever be pushed again, and he learned the limits of his own abilities, which were far greater than he would have believed otherwise. Overall, he's glad he did his PhD even if there was a lot of suffering and struggle.
An (actual) close friend of mine had an advisor who had himself been a student of a Nobel laureate. The relationship was primarily of the second type that you describe - lots of cheerleading and encouragement. But there was certainly an element of discernment which I think was passed along. I remember distinctly that my friend was extremely skeptical that his paper would be accepted by Science (the journal) but the advisor instructed him to submit it; the paper was accepted. So now my friend has a publication in Science basically just because his advisor had the judgement to know when something is important enough to submit to Science. This may seem like a small thing, but having a Science publication is not a small thing, I think.
And I realize this is all highly anecdotal, but I can definitely attest that I have neither seen nor experienced any kind of mentoring relationship similar to either of the above since I left Academia.
Among my friends interested in rationality, effective altruism, and existential risk reduction, I often hear: "If you want to have a real positive impact on the world, grad school is a waste of time. It's better to use deliberate practice to learn whatever you need instead of working within the confines of an institution."
While I'd agree that grad school will not make you do good for the world, if you're a self-driven person who can spend time in a PhD program deliberately acquiring skills and connections for making a positive difference, I think you can make grad school a highly productive path, perhaps more so than many alternatives. In this post, I want to share some advice that I've been repeating a lot lately for how to do this:
That's all I have for now. The main sentiment behind most of this, I think, is that you have to be deliberate to get the most out of a PhD program, rather than passively expecting it to make you into anything in particular. Grad school still isn't for everyone, and far from it. But if you were seriously considering it at some point, and "do something more useful" felt like a compelling reason not to go, be sure to first consider the most useful version of grad that you could reliably make for yourself... and then decide whether or not to do it.
Please email me (lastname@thisdomain.com) if you have more ideas for getting the most out of grad school!