Not the parent commenter, but I agree with the sentiment. The selected portion of the earlier comment has multiple pieces that I disagree with: 1) A PhD isn't about writing, and 2) you are not expected to become a professor once you get a PhD in the US.
A PhD isn't really about writing, it's about research. Writing is merely the means of demonstrating that you know how to do research. The way that you break something down involves finding a gap in understanding or a portion of a problem that has not been addressed. Then you find an insight that leads to potential solutions to address the gap. Then you run experiments based around the insight. It is fundamentally a way of thinking, not a way of writing. That's why it's a Doctorate of Philosophy. The actual topic that you cover for your thesis is not as important as the demonstration that you know how to think about research. It's moderately unlikely that you will be working on the same problem in industry.
It's commonplace, at least in engineering programs, to ask whether you're going to go into industry or academia. Research positions in industry typically go to PhDs or Masters with a lot of experience. It is much harder to break into the research world without a PhD in the US. So I believe the original statement:
> a full-time professionalized pursuit under the assumption you will be a professor
is overly specific. Your future could be a professor, a researcher/scientist, or an entrepreneur.