What is more serious a situation, being possessed by an unearthly entity, or

In my worldview those are the exact same things. I get my concept of possession from the original Greek daimon. Which was ones guiding principles or even soul according to one definition.
The idea of a Christian demon is more like someone stole your car and all you have to do is scare them with Jesus to get it back. Ever tried to get a personality disorder out though? That stays in there. You can't deposses that.