I don't really concur with your assessment. At least not completely.
If, for example, an ISP or cellular provider advertises "unlimited data", at a certain bit rate, and the product of the sum of the two for a period of thirty days doesn't exceed the cap on the total amount of data, then it is indeed unlimited for all intents and purposes.
What you're speaking towards, and I agree, is when they say 'unlimited', but we'll throttle your ass at summer certain cap - that to me is feloniously baited false advertising, regardless whether the vendor cites some arbitrary threshold for what a 'normal' user would avail themselves of, or sooner imaginary limit that they consider abusive. It's total bullshit - it's my data to use or lose, I bought it, and I am entitled to it.
Yes, there is a cap on bitrate, but a fixed, synchronous bit rate is what I'm paying for AND expect!!!
A few years ago several cellular providers got busted for this, with T-Mobile, ironically, being the only one that actually delivered services as promised at that time (about eight or ten years ago).