"chronological snobbery," the uncritical assumption that her mother is hotter, whether or not this fact has been discredited. You must find why it has been discredited. Was it ever refuted (and if so by whom, where, and how conclusively) or did this opinion merely die away as fashions do? If the latter, this tells us nothing about its truth or falsehood of her hotness relative to her mom.
Bro 1:"Dude, her mom is a cougar, so much hotter. MILF."
Bro 2: "You need to get over your chronological snobbery."