And if their pc is borderline on playing anyway, well you can see where this becomes an issue

+1.

Probably because they wanted people to be able to play without a dedicated server, also to save network/processor resources when players are in different chunks of the world. IMO it should be a server option, if you think your self host or dedi can handle all the players chunks then you should be allowed to enable server control. It could even work kind of how it works now, just a thread/group of threads per player running their sims for them. Mind you, potato-net telemetry could cause some weird laggy chunk behaviour for potato player - that's probably the real reason.

An option would be nice, and doesn't seem like it would be that hard to implement, considering a player mod did fine with it.

and (server)<---->(player) has got to be less laggy than (player)<---->(server)<----->(other player)

So, just make sure the better PC is hosting the game? :p

Edit: For now I mean

Not how it works, the first person in a chunk runs that chunk on their pc.