What happens when kids don't get it that lesson, or that week. How do they catch up?
Personalised learning is much more "personalised catch up".
One thing that struck me recently on "The rest is politics" podcast is old Etonian Rory Stewart explaining that his (posh private) school he would get up about 8 and go to bed about ten and the whole day was full of structured learning / events. That (top) private schools might get better results simply because there is 2x or 3x as much teaching going on.
Perhaps the answer to school is simple - spend 2x to 3x more. we might not like it. But maybe it seemed ridiculous to pay for schools and books for Victorian children in Dickens' day as well