While there are certainly benefits, I can't agree that YouTube loses nothing here. PeerTube is a potential competitor in an ecosystem that's currently functionally monopolistic, and even in a vacuum, having a nontrivial community move to that platform will immediately increase awareness and provide legitimacy.
Perhaps more importantly, the FOSS and tech communities are not a vacuum. Google and YouTube in particular have been getting increasing amounts of negative press recently, and this strongarming of Blender further drives home how far they have gone from the era of "Don't be evil." Additionally, the precedent of changing platforms rather than giving in to Google's pressure has now been set; While there will be no mass exodus, it is easier for entities to follow in Blender's footsteps than it would have been to set the lead, and we may hope that this move turns out well in order to further encourage others with similar inclinations.