> Given that nobody has found concrete evidence of any phenomena being supernatural ever,

I'm going to take issue with this. Anytime we sufficiently understand something it stops becoming supernatural and becomes natural. For a long time lightening, and disease were considered supernatural.

To assume there cannot exist things or beings we do not yet understand about the universe simply because we cannot explain it is the height of huburis.

I don't think "anything we do not understand" is the commonly accepted definition of the word "supernatural". It certainly wasn't the one I was using.