You’ve substantially moved the goalposts. Your argument about the French Lit. PhDs involves understanding the field at a roughly undergraduate level not producing new work. Developing a deep enough understanding of physics to create novel ideas in it is far harder than this. I’d argue that producing relevant new work in French Lit. is easier because of the high degree of subjectivity creating a low bar for relevance. The low bar for relevance makes it far easier to be novel since one can explore almost any tangential point of the work one can imagine. It’s far harder to come up with new interesting ideas in a field where ideas have standards of correctness than in a field where it’s sufficient to be novel and vaguely relevant.