Youtube is the real tough one to replace, BiliBili is probably the only one that comes close to it and it's Chinese.
One way out of this would be if content creators would en masse upload to multiple sites. Even with preferential treatment for YouTube, this would enable consumers to follow their favorite creators outside of YouTube, and get the same content. Of course, this onus is now on the creators, and I imagine they have enough to manage as it is. So what they would need is a good incentive. But that is people, and as long as they have enough people on YouTube, there is no incentive to diversify. So we're back at the network effect.