"I'm skeptical that photoreading books without bothering to think about the content is the answer."

I didn't say you don't have to think about the content.
I said you don't need to think about EACH idea.
The material you have to focus on is the material fitting to your purpose.
Anyway...I'm talking about the whole system.
During photoreading phase, just relax and .... feel your purpose.
Don't think at contents.