I think scale matters because almost no person is as much of an island as your example fishing video guy. I actually have noticed almost the opposite in most people I know, YouTube is the default place to get entertainment. Across all their interests.
From both sides the network effect might be strongest with YouTube, the creators can’t leave because YouTube has virtually all of the audience, and consumers don’t want to watch singular people on other platforms because on YouTube you can stumble over interesting videos and all the people you like to watch are already there.
The only way I see for other platforms to actually grow is forced interoperability, as in videos of other platforms appearing in the YouTube frontend. Which Google would never do so the government would need to force them.