You argued with opinions and unsubstantiated statements, not facts. Youtube and Facebook overlap significantly in many ways even if the user markets are not identical. The point is Facebook (and other social networking sites) can be used to reach a large audience with video content. Just because Youtube is a media website does not mean that it is not a social networking website and just because Facebook is a social networking website does not mean that it is not a media website. Youtube did not start out as a social networking site but it added such features over time. Facebook did not start off as a media website but it has added video features including large video uploads and live streaming.
Youtube is a free to use video service. You have other viable choices with a significant audience, therefore it is not a monopoly. Even if the user base of these other services are smaller, they are still significant.
But for a more direct comparison with some actual numbers, according to Wikipedia Youtube has 800 million unique monthly users. Daily Motion, just one direct competitor to youtube, has 300 million unique monthly users. Obviously youtube is more successful but it sure isn't a monopoly. I don't agree that 300 million vs. 800 million is a "pittance". If you don't want to consider youtube a social networking site (it has all the elements so I don't know why it wouldn't be), then here is a list of sites that are video related: https://en.wikipedia.org/wiki/List_of_video_hosting_services (facebook is on this list too).
A couple of other's with significant traffic:
LiveLeak: 45 million+ unique monthly users
Vimeo: 100 million+ unique monthly users
Facebook: 2.2 billion unique monthly users
Then new services such as DTube and bitchute are popping up all the time. Their success remains to be seen (Bitchute already has ~30,000 unique visitors per day).
Incidentally, the definition of monopoly (according to Merriam-Webster) is: "Exclusive ownership through legal privilege, command of supply, or concerted action". So it's more than just "most successful by a lot". So even if I agreed that those other options combined were a "pittance" compared to youtube (which I do not) then that still wouldn't make Youtube a monopoly.
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