I don’t know what YouTube’s market share is, but for videos that are not short TikTok style it’s probably like 95%? And they are also in the TikTok short and twitch streaming areas now, so I think it would be a massive blow to video streaming if they went away.
BitTorrent just moves all the costs to the users, and users are typically not wanting to run their own video servers. They might work for tech people who don’t mind running servers or already have a server they are running, but you have to think about the regular user that is probably 80% or more of the market. You can’t expect to get big off relying on users to be the servers.