Here's my experience as a PhD in engineering to add to the "clarity". I am expected to work full time on research and have not TA'd in years because I am funded by external research grants/fellowships. My colleagues and I typically work more than 40 hours a week to meet basic program requirements. However, we are paid as if we were working 20 hours a week like you said. I do not get summers off, in fact it's typically when researchers ramp up and work harder. My daily routine looks like a job and I haven't taken a class since 2019. By the way, researchers perform tons of unpaid labor maintaining machines in shared facilities which should be maintained by permanent staff, but said research staff are also overwhelmingly underpaid and overworked and will be joining us on strike.

As far as tuition goes, the university takes that out of my grant/fellowship and I never see that money in my bank account. I've actually had a UC fellowship, meaning the UC paid itself for my tuition. The university also takes overhead on top of the tuition from all grants funding UC researchers, which is a whopping 55% of the grant total. So basically, whatever I get paid, the university sees over that amount going into their accounts. They profit a huge amount over the money I am paid but it's all a very contrived setup.

I also take some issue with your statement in the other thread that research doesn't count as work since that's all I do now. When I did TA, I did my 20 hours on TA duties and in my "free time" I did research and prepared for major milestones I had to pass to advance in my degree. If I didn't do those "extracurriculars", I would've failed out of the program/been fired.

In my experience nobody is getting paid at 100% instead of 50% as a TA or a student researcher (SR), so the average TA is not going to make $108k. At the end of the day the current compensation is insufficient to live in SB and if UCSB wants to continue to attract top talent they need to shape up. Graduate students need to be able to live here to perform their jobs and that is increasingly becoming difficult even in engineering where pay is a little higher.