It is in a perfect market, but Google holds the monopoly and the game is set against competition.
For online ads? Sure you can make that case.
Their business in the end is based on delivering relevant content. If there is a market for the traffic Google refuses to host, then there are probably market opportunities there.
1. When you buy an Android phone there's a good chance that YouTube app is preinstalled.
2. If you search the net for "how to do XYZ" or for any song you'll get 99% video results from YouTube.
3. Almost every company/celebrity/influencer/... has a YouTube account and until recently (TikTok, Odysee, BitChute,...) alternative platforms (Vimeo, Dailymotion,...) were mostly a niche market.