Even dedicated circuits do not guarantee a certain speed 100% of the time. They guarantee a certain speed 99.x% of the time specified by an SLA.
> Verizon doesn't have any consumer plans that guarantee both an amount of data usage and a specific speed.
They do. They have multiple plans that specifically say "Unlimited 4G LTE Data"[1]. You might argue that 4G LTE is not technically a measure of speed, but it is certainly understood that way by consumers, so it should not be used in marketing if it is not intended as a measure of speed.
Even if it's hard to exactly quantify a priori what "4G LTE" speed is given that it varies with circumstances, it's pretty easy to show when Verizon isn't trying to deliver as much data as they have capacity for. The fire department did that, by comparing speed on their throttled device side by side with a personal device on the same network.
The problem is that there is a well-established distinction between a dedicated circuit, which offers a certain speed "all the time," and best-effort service, which offers "up to 50 mbps" subject to network congestion. To anyone familiar with telecom, it sounded like you were saying that only e.g. 50-mbps dedicated circuits should be advertised as "50 mbps."
I agree with you that if you advertise a 50 mbps best effort service, and also guarantee unlimited data usage, it would be wrong to throttle it after a certain amount of data usage. But to my knowledge, nobody does the combination of both.
> Verizon has multiple plans with "Unlimited" (some of them with the ridiculous names of "Above Unlimited" and "Beyond Unlimited")
Verizon doesn't have any consumer plans that guarantee both an amount of data usage and a specific speed. The plans that specify a certain speed (e.g. FiOS) do not throttle after any amount of data usage. The plans that specify unlimited data usage with throttling after a certain point do not guarantee any particular level of speed. You're taking "unlimited" to mean "without limits in both data rate and data usage," which is one possible, but not the only possible interpretation of the phrase.