It depends what you're looking for, though. The last 10% is heavily on the writing up and justifying independent research part, with some academic politics thrown in (convincing five professors to sign off on your thesis is not as objective a process as one might think). If what you want is someone really good at applying research, perhaps with clever tweaks, that part might not be as important. That's one reason places like Palantir explicitly recruit for "all-but-dissertation" PhD students. They need the kind of knowledge that someone will get from being in the research world for 3-5 years, but their needs aren't quite the same as someone hiring for a professorship.
"The last 10% is heavily on the writing up and justifying independent research part, with some academic politics thrown in....places like Palantir explicitly recruit for "all-but-dissertation" PhD students. They need the kind of knowledge that someone will get from being in the research world for 3-5 years"
That's called a Master's degree. You take some coursework, learn how to read papers and implement the ideas therein. It's a fine degree, but it's not even remotely the important part of a PhD.
People who actually go through the "writing up and justifying independent research part" of a PhD tend to find that the writing and justifying are the hardest part of the technical process. It's easy to brush it off as minor, but only once you've begun writing and organizing do you realize the places where your work falls short. The writing takes a long time not because it's especially hard to write a dissertation, but because you usually have to go back and deal with a lot of unanticipated technical problems before you can say the work is done.
Well, I'm writing up currently, and I guess I don't consider it the most important part, really. I'm finishing it more because I want the Ph.D., not because I'm learning anything at this point.
Perhaps you could get the deep research engagement via an unusually research-focused master's, but there usually isn't scope for that. An M.S. is normally only two years, while 3-5 years is imo the amount of engagement you need with a field to really understand what's going on in research. You need to attend the major conferences in a field more than once, ideally present papers at several of them, present a few more papers after the initial time you do (your first presentation is never the greatest engagement with a research community), and so on. You can get to that as an ABD PhD student, but rarely as a master's student. An M.S. student publishes between 0 and 1 papers typically, and maybe attends 1 or 2 conferences, while a 5th-year PhD student, in CS at least, will more typically have published at least 3 papers in major venues (often 5+) and attended 5+ conferences.
That's all still writing-and-justifying independent research (getting a few conference publications and journal articles), but not quite the same as writing the equivalent of a book, which is a fairly different skill, and one you're not actually likely to use again after getting a Ph.D., since most research is done in conference and journal papers. I wouldn't say it's a complete waste of my time to be writing a thesis, but I wouldn't say it's the most important thing I've done in grad school either, by a long shot--- I value my peer-reviewed publications in the scientific literature much more than I value my institution's thesis/defense process.
I don't want to appear too critical, but you've just outlined the reasons not to persevere with the write-up. The point is that you are right in every respect : except for the part that doing the last 10% is only a modest amount of work.
With luck, you've got enough momentum to push through to the end smoothly. Otherwise, you might find yourself within 'just a short distance to the summit' and being someone that climbed 90% of the way up Everest.
