Minecraft isn't an MMO, it's a completely playable stand-alone game, with multiplayer aspects. Completely different paradigm, utterly incomparable in execution.
Also, you have to manually add -all- servers to Minecraft, which is exactly what I suggest for anything beyond "vanilla"; the browser shows all the verified baseline servers, and adds the option to add modded/customized servers to a uniquer list (just like Minecraft)
Yes, yes it is. Even single-player worlds have the option to open up as a multiplayer server at any given time, rendering that argument null.
And manually add servers to where, exactly? Rust is actually easier to run a server off of, because there is a single concise server list implemented within the vanilla game. In Minecraft, you simply create or purchase a server, and then you have to advertise like mad just as one has to in Rust.