As for Agent Smithing
Well, think about it this way: You want to be able to play with your friends, right? But on the other hand, you want the universe to be massive. Like the kinda massive that takes hours if not days to cross. Now, say you've been playing with your friend for a bit on one quadrant, your friend logs off but you still got time so you continue playing. Will you just stay in that one quadrant so the next time your friend comes on it doesn't take 2 hours for you guys to meet up? What if you got on a dynamic event stream that would take you to another quadrant, will you skip on that and instead hang around where your friend will eventually log on? That's the kinda shackle that would likely dampen anyones enjoyment. Or maybe you just have more than 1 friend and it's impossible to keep everyone nicely grouped up in the universe.
So, how to solve that in an immersive way? The world can't have teleporters, that'd kinda make the whole wormhole thing pointless, not to mention cargo hauling. Now there could be some other solutions, but temporarily playing as another character seems like a pretty good balance between immersion and facilitating playing with friends.
(Also, if the universe was so small that you could just meet up with anyone anywhere within few minutes, where's the immersion in that? Would also make any strategizing for wars kinda moot, if all the troops can be basically anywhere at any time. The universe has to have some meat around the bones)