That’s an argument for bandwidth caps, not data caps.
...while those who know they'll hammer it more than average have a specific idea of how much they can get away with.
If you use traffic when the network is congested, so is everyone else who is active when the network is congested, so you should all get an equal share if you're paying the same monthly fee, and a share proportional to your max connection speed if you're not. Nothing to do with how much you used when the network was idle.
For instance, if you maxed out a 100mpbs home connection 24/7 for a month, you could transfer no more than ~32tb.
I’d suspect data caps are useful for over sold areas, but are great for lining the pockets of greedy ISPs.