Thats not proof.
its like saying the freeway is full of traffic, and using a vpn would be like taking only side streets.
Its a matter of how your traffic get thier.
I highly doubt they are intentionally throttling.
I know (fairly sure) in my area At&T has a YouTube cache setup, those videos LOAD damn fast, but obscure videos don't load as well.
YES they could upgrade their infrastructure but thats a whole other problem.