A phd in particle physics (even from caltech) can be as meaningless as journalism from yale/harvard. Entire careers have been based on strings ...which is famously not even wrong.

As in every profession, there are lots of "artists". Some also have substance though: ie. Feynman was like Dali: some neat stuff (teaching) and some less neat1, to still make a living.

1 ,,Please send my notes back'' -- Stückelberg (not the painter), as his worst enemy used to joke (back) to him

I disagree: you definitely have to be able to understand lots of complicated stuff to get a PhD in astrophysics from a place like Caltech. And even if string theory isn't physics (i.e., doesn't make testable predictions) it still is a kind of math or at least inspires a lot of math.