I stopped using NetworkManager years ago, I just use wpa_supplicant and dhcpcd directly (well I use the systemd services for these so they're started automatically). I also always name the 2.4GHz and 5GHz networks differently, and connect explicitly to the one I want.
Yes it would be great if NetworkManager did the right things automatically, but the task might be impossible due to hardware and driver quirks. WiFi chips are among the buggiest chips in computers today. Really, the chip. I've seen ridiculous workaround in drivers for multiple vendors' chips. Also, the drivers are complicated and buggy. And the linux drivers don't get quite enough full-time attention from the chip vendor to work solidly. Those windows and mac wifi driver teams are pretty big.
Yes it would be great if NetworkManager did the right things automatically, but the task might be impossible due to hardware and driver quirks. WiFi chips are among the buggiest chips in computers today. Really, the chip. I've seen ridiculous workaround in drivers for multiple vendors' chips. Also, the drivers are complicated and buggy. And the linux drivers don't get quite enough full-time attention from the chip vendor to work solidly. Those windows and mac wifi driver teams are pretty big.