The atheist mistakenly assumes that if something is not known or cannot be known theoretically, it is not worthy of belief. Once again, a belief in only what the individual or collection of individuals think, know, perceive, or feel. The unknown is not the same as unreal.
I largely agree with your post. I particularly agree with the general point that belief ('faith') is an essential part of being human. It is a source of energy. Despite welcoming the collapse of Xtianity, Nietzsche, for instance, wrote of the utility of belief for driving human mind to higher endeavors.
However, keep in mind that Atheists, on an underlying level, have their own faith and their own mission. They are driven by belief. You cannot 'know' (in sense of having a 100 per cent certain true belief) that the supernatural does not exist. You are simply driven, if an atheist, by the conviction that physicalism captures the stuff the cosmos.
This is not
to say that most of the objective evidence does not point towards a physicalist ontology... but just that it does so probabilistically, and not with 100 per cent certainty.
The premise is simple: the unknown is not a lesser aspect or lesser part of reality, if anything it is primary. For every one thing that is known, there are ten things that are unknown. What you don't know could fill a library.
Yes, the unknown is like an open ocean to an explorer, or a christian village to a Viking.
However, do not conflate the unknown with the known-probably-not-to-exist.
It is one thing, from the point of view of knowledge, to not be 'captured by human minds' because you are yet to be reached - another not to be 'captured by human minds' because you don't exist.
Something that is beyond your grasp you cannot put in a basket, alternatively you can't put what doesn't exist in your basket either.