You started this thread by saying

what’s the concrete advantage of the average person reading at a high level is, past some sort of weird elitism?

and now you’re trying to point out that grade level isn’t a good metric. So is it that reading level doesn’t matter at all, or that the metrics we use are flawed? Reductio ad absurdum, is it ok for an entire populace, or at least the vast majority of it, to be illiterate?