Today I learned that Runescape is where the real men write backend game servers.
In practice it wasn't utterly horrible to play this way, it was just very surreal to be running around engaging in combat with name-plates floating in the void.
But, that method is difficult to get right in Unreal Engine and impossible to do with Unity. That's why you only see it in high end titles like Battlefield but not in any indie MMORPG.