The deliverable from a PhD in my discipline is a dissertation. You might also have book-chapters, articles in a journal, essays for the general reader, or even a book.

All of these have one thing in common: words. No matter how good or bad your thesis is, everything boils down to how you present it; that is, how you write.

So, rather than imagining a PhD as a 80-20 split of thinking and writing, it would be more useful to imagine a 0-100 split of thinking and writing. But of course, you can't have 0 thinking. What I mean is that think as much as you need to, but the finished product is not your thinking but your capturing of it in words.