There are also plenty of anecdotes of people who self-profess that for years or decades they couldn't wrap their head around some math concepts, and then one day they met a teacher who explained it in a different way than any teacher before had done, and it "clicked" for them as adults.

I don't know how to weigh these anecdotes, but I think that's suggestive that the methods of teaching might be relevant even to people who struggle with math for decades.