That is right. And while it theory having a separate executor (eg in the futures lib) and IO providers (timers, sockets) in another lib works it will in practic

That is right. And while it theory having a separate executor (eg in the futures lib) and IO providers (timers, sockets) in another lib works it will in practice never be as efficient as having an integrated system like Tokio. The reason for that is that decoupled solutions can’t integrate the reactors in the same eventloop and there is always extra synchronization and thread hopping involved. The difference can be huge, eg 50% less throughout on a server.