Right... You're missing the point entirely.
The only limit to T-mobile's unlimited 4g (not the tiered plans for which they do state limits) is their network capacity. They prioritize based on usage, but that's not a limit, it's prioritization and, in fact, it improves network performance, even for the deprioritized users, by reducing competition for a scarce resource when there's not enough to go around, allowing lighter users to finish their downloads faster and get off the network sooner.
There is no speed limit here, nor a time or usage limit.
Consider this: If they didn't have the deprioritization policy, excessive congestion on a given tower would result in a completely unusable connection for everyone. Giving a subset of users priority to allow them to get off the network sooner avoids that; it effectively increases the speed limit for everyone by more efficiently utilizing the available bandwidth, which is limited by physics.
If you've never implemented proper QoS on a congested network and seen the immediate impact it had on the traffic flow, this isn't something that is obvious to most people, so i fully understand how you might think it's a limit of sorts, but the reality is that it enables all users to effectively get their data instead of flooding the data with retransmitted packets as everyone attempts to talk over everyone else.