That's kind of my point, ISPs use that max speed in their advertising when it isn't really relevant, especially if it hits your cap in a minute or two.
It is relevant, though. I have 1.2 Gbps down with a 2 TB monthly cap. I've never hit the monthly cap even once, but by your standard I have "1.2 Gbps down for 3 hours, 42 minutes".
But that doesn't change the reality that it matters to me that a 20 GB video that a friend took at my wedding downloads in just 2 minutes rather than the ~30 minutes it would take if I had a 100 Mbps connection.
So telcos can advertise "Up to 200Mbps" for their package.
But then if they have a 2GB cap, they also need to say, "Caps at 80 seconds of usage".
Because that's what you're paying for at that speed, 80 seconds of usage per month.
Sure, you're not always (or indeed never) doing 200Mbps, but then you're not getting the speed you paid for.