I don't know how to solve this problem.
When the network effect shifts, it does it gradually with long siphoning effects, not all at once.
People use gmail for free, and there are no network effects.
Content creators use YouTube due to its ability to sell ads, but I am not familiar with the alternatives to know if they are capable of handling the amount of people and ads YouTube serves. It seems like a more difficult problem than alternatives to email/maps/drive/search.
huh? There's a massive difference between those two things. YouTube provides discoverability for your content. Gmail does not. Besides the loss of existing viewers in a platform switch, creators would also lose a huge audience of potential viewers of their content both from recommendations and from search results. Sure, there are content creators who build up followings, but lots of people will get a handful of videos that become popular results for certain searches. Those come entirely from searches and "related" listings.
Further, changing emails doesn't require people emailing you to use a completely different client to do so.
What about Vimeo? Or for a more federated approach, PeerTube?
From the last conversation I had around PeerTube, the main objection I got was that content creators would probably lose a bunch of traffic which they switched, which is true, but that's effectively the same argument as the hassle involved with switching off Gmail.