PhD students should be employees with all of the protections this gives them. They should have unions (I have been both at union and non-union shops, you want to be in a graduate student union). PhD students should benefit from the combination of protections given to students and to employees.
Students should get paid a living wage. The problem today is that NIH, NSF, DARPA and others refuse to give us funds to pay students reasonably. I cannot write an NIH grant to pay a PhD student reasonably. Literally. My grant will be rejected because I'm paying too much. I can't pay postdocs what they are worth either for the same reason.
For better pay, you need to lobby Congress to beat NIH, NSF, DARPA and others with a big stick until they stop this system of abuse.
If you want to end advisor abuse it's simple: PhD students should not be tied to advisors. Under a system where your funding depends on one person, you always suffer from a power imbalance. PhD students should be free agents. When you join, the university promises you 6 years of funding and checks in every 2 years. Go nuts.
As for the thesis? Even in STEM a thesis is important. But, what a thesis is has changed. Today you often staple together 5-10 papers that you published. That's great!
PhD overproduction?! Nonsense! We don't have nearly enough PhDs. The demand for PhDs in industry is huge across many fields. It's true that in some fields there is too much supply, but there's also an oversupply of people of those majors in general anyway, that's not an issue with the PhD.
PhDs are critical for the development of humanity. It's a system that takes a smart person and turns them into a capable smart person who can find hard new problems and solve them.
There is absolutely no reason why we can't unionize all PhD students, immunize them from advisor influence, and pay them a living wage.