I did not ever, at any point in this thread, contest what you are saying.
I agree with you.
The tiered caps are specifically for saturation issues and not COST issues.
Yes, it is for saturation, but that becomes cost when the carriers have to add more cell sites to handle the increased data use.
I expect to see, perhaps at 6G or thereabouts, a move to micro-cellular systems where the number of cell sites is increased substantially even to the point of having one or more cell site within an office building. This way they can operate at lower power and increase the bandwidth in a larger area by breaking it up into many smaller areas to reuse spectrum.
To do that, of course, will require a big increase in network costs that will be partially offset by lower per site cost. In major urban areas where higher frequency cell signals (4G) don't propagate as well we could see one or more cell sites per floor of major office buildings.
Alternatively, a next generation cell phone maybe able to use wifi to do everything it now uses cellular networks to do so that the cellular bandwidth could be supplemented by wifi. If the hardware/software is available on the phone you could configure it to use your home, office and other wifi systems to offload bandwidth requirements from the cellular network.
In the mean-time, however, the carriers will have to deal with the legacy of there "unlimited" plans and the tendency that many have to overuse the network because they can.
Brian