My PhD mentor was actually great. Seriously.

I have a somewhat abnormal training history. What you are suggesting wouldn't have protected me from the long term trauma I endured working in a lab for 11 years starting as a freshman undergrad at a PUI that transitioned into an R2 institution over that time period. I was young and naive enough to not even realize what they were doing to me until years in and then I was too scared to leave (because the PI was "a very important and influential person and if I left no one would ever hire me and my career in science would be over" - remember PUI-to-R2...asshole). As the years went on I eventually began idolizing the PI as if they were Gods gift to science and the world. I know that I only got out 11 years after starting my undergrad and after I finished my master's because they retired. They mindfucked me so deep that it affects almost all aspects of my personal life and I still have to go to therapy for it even now in my postdoc. The worst part about it all was that the entire department knew what was going on and even told me after he retired how much fucked up shit they saw happen to me, but didn't do anything. Why? Bc my PI wasn't just the PI of a lab, but also the individual that makes final decision on tenure for the entire University (say it without saying it). So again for me, what you suggest wouldnt have been able to protect me. I was fucked from the moment I stepped foot into that lab. It must have been my fate.

My comment isn't for obtaining sympathy and certainly not pity. Monsters are everywhere and I just happened to encounter one at a much too vulnerable time in my life.

My point is that there is a system in place in academia that is very broken that extends far beyond treatment of PhD students.