It's just one of the many things that show the dev process never really had people having more than one character in mind.
You can't have multiple characters logged in on the same service account, the very reason why you can't friend your alts - why you can't send them mail or add them as a tenant to your one personal house per service account (I get why that limit was needed, I don't get why all characters on your service account don't default to tenant status if the game already knows the service account has a personal home on that world).
As far as congestion goes, it doesn't matter if you have 1 character on a world or 8, if it's the same service account you can only ever have one of them logged in.