Lower frequencies definitely pass through material better and generally have longer range, but with mesh systems you only need half or a third the range, becaus

Lower frequencies definitely pass through material better and generally have longer range, but with mesh systems you only need half or a third the range, because you've got repeaters. 5Ghz still goes through a few walls, kinda, mostly, so you can use it for closely spaced repeaters, kinda. Which also means the 2.4ghz part can be turned down a lot, because it's only got to go to the nearest repeater, if you even need a 2.4ghz link at all for anything but IoT. None of this applies to typical HN readers though, who all seem to be running an HFT stock exchange in their basement and need 10gbit at 0.5ms latency, but for the rest of us if it's good enough for 1080p Netflix and 720p zoom calls it's perfectly fine. Except when the printer disappears despite everything having a strong signal because of mesh bugs... then it's not fine.