There is No True Unlimited any more even on ISPs. So they should stop using that phrase for all time. On a broadband Internet provider you can use a couple hundred gigs before they start sending you warning letters. I can binge watch a ton of my favorite shows and movies on Netflix in HD and not go over 150 gig on Charter Communications. If your using 500 gig a month or more your either streaming 4k video or downloading a ton of files off The Pirate Bay. Mobile isn't designed for this. The Phone Networks have a right to crack down on abusers of their Networks. The abusers can and should be put out to pasture and Good Riddance. Hasta LA Vista and don't let the door hit you on the way out. (SLAM!!!)
UNLIMITED — look it up. If a company is going to start taking action against you when you go beyond a certain LIMIT, then there is a problem with the marketing. It doesn't matter what someone is downloading or why. You're starting to make the argument that certain types of internet use are more legitimate than others? Are you going to police what is ok for a home user to download/upload? What if I want to stream my life to the world 24/7 in 4k from multiple vantage points? What if I want to attempt to assemble a database of every image ever posted online for my deep learning system? I should not need to ask my ISP for permission to do this stuff on my "unlimited" connection. If it's going to be a problem for the network, then they should probably use a term other than "unlimited" in the service agreement. That's all this article is saying.
Regarding the tethering, there is absolutely no reason the mobile provider should treat data transferred to your phone differently than data transferred to your computer. As the article states, if they want to set a limit on the connection, then set a limit right out in the open where everyone can see it and agree to it, and stop pissing and moaning about people attempting to use the service they pay for in whatever manner suits their needs.