"What happens when multiple devices in your /8 want to listen on port 80 and 443 on the public address?"

This is a feature not a flaw. The average person doesn't have anything acting as a server, and that's a good thing, because the only servers they'd have would be embedded garbage in poorly maintained or completely abandoned IOT devices with incompetent code that should not be publicly exposed, ever, in anything but a call out model.