The no justification applies whether it's a for a supetnatural concept or not here. That said you are right if a supernatural claim is involved then there is no such process. I would suggest intersubjective rather than objective.
Since the belief is based on nothing, other than telling me what the person believes, it seens to have no value. What definition of worthless do you think means it isn't?
I would agree it has no value to you. I assume it has a value to the person who holds the belief otherwise they would not continue to hold the belief. So just clarifying it's a subjective assessment of 'worthless'. I would say the belief is based on something that cannot be demonstrated to someone else.
Also I would say that someone else might not necessarily see the value even if it could be demonstrated, including other theists as well as atheists. So a Christian might hold a particular belief about a supernatural entity, wouldn't be able to demonstrate the value of this belief to another Christian who holds a different belief, and even if they could demonstrate the value to them, it might not seem of value to the other Christian.
This could apply to all beliefs I suppose - even if you could justify or demonstrate how you arrived at your belief, your belief might not be of value to someone else, so they wouldn't adopt it as a belief they hold.