Youtube is anything but centralized, they literally pioneered distributed video content with their GGC nodes, with at least 10s of thousands of nodes all over the world. They may not be the first, but almost definitely the largest.
I don't understand why you are mentioning peer to peer technology? What does that have to do with anything? Youtube is not a cute side project where your viewing experience depending on how many peers your video has. Peertube depends on webtorrent, you literally have to host and seed every single video on your platform and duplicate it multiple times by others. Good luck doing it over petabyte scale. Google does something similar, but popular videos are hosted at users-end point on GGC nodes, distributed over 10,000s of servers all over the world.