I feel like I'm not making myself clear. It doesn't matter how large and great is the last mile infrastructure to the neighborhood. The ISP itself has limited capacity; their pipe to the internet is only so big, and all their customer bandwidth runs through that pipe.

ISP capacity does NOT cover every single one of their clients using 10 Gbps at the same time by a long shot. Most ISP can maybe cover 5-10% of their total advertised speeds at any given time. That's why they say "up to". They can do 10 Gbps simultaneously for a handful of customers here and there; if everybody starts using the internet at the same time (evenings, the weekend) the speeds drop dramatically. If any significant portion of their customer base ever happened to use the internet for anything serious at the same time it would be a shitshow. Every ISP bets on that never happening.

So getting back on topic, this kind of throttling typically does not fall under net neutrality. It's not discrimination based on where the data is coming from. You could argue it's deceptive practices or false advertising but that's a different kettle of fish.