> 3D graphics, in distributed systems, in machine learning, or other "hard computer science" fields

You're looking across widely different fields that are each impossible for anyone to master (despite the degree being called a Masters).

To use an analogy, even the GOAT Michael Jordan couldn't transfer his skills across sports.

You could pick anyone of those, spend an entire lifetime (or several) and barely make any impact.

If you want to develop expertise in any field, go right ahead. But the idea that a PhD (or anything) would allow you to master multiple tech disciplines is a pipe dream.