Let's say, hypothetically, that I create a website that rivals YouTube where people do achieve fairly consistent success, and can live off of the income from their videos. What do we expect to happen?

Hundreds of thousands of people will try to get in on it, causing both the income of existing creators to drop, and the average income to plummet.

Any market where there is a huge supply of people who want to produce the good is going to have this problem.