I don't agree with you on tethering - it's an explicit violation of the TOS, and if all data was truly equal then you wouldn't need to consume it on other devices. And that's what their plan basically did, giving you truly unlimited, unconstrained data ON THAT SPECIFIC DEVICE. VZW never sold or represented the agreement was unlimited data piped to any and as many devices of your choosing.
I'm not going to watch a movie on my phone when my 55" tv is right in front of me, so that's why my usage would increase with tether if I can pipe that data to my tv. It's not that the data isn't the same, it's that I'm connecting another device to their service I haven't paid for - note that shared plans have a charge for each device connected.
Very simply, VZW knew not allowing tether would arbitrarily cap how much data the vast majority of people would use, which allowed them to offer unlimited. Because most people were not going to use a much smaller and slower device when better options were available...but then phones started getting huge
So now you have people legitimately using 10-20GB a month without tethering.