Nothing in the formation of the universe comes anywhere close to proving supernaturalism. Supernaturalism is not a part of the rational world. You have yet to even define supernaturalism and how that would apply to the rational world.The origin/creation of our universe is an example of a verifiable supernatural event - depending on your definition of supernatural.
Our universe is precisely fine tuned in many ways to allow for stars and life as we know it to exist. Our planet is fine tuned so that life on the surface of the earth could exist.
For example, the precise fine tuning of the expansion rate of our universe (Isaiah 40:22,26) allowed stars to exist, which allowed supernovas to exist which allowed elements other than Lithium and Hydrogen to exist .....
The Big Bang theory has some elements of truth to it (pun intended) but it does not explain many things including the crucial one: the actual origin of our universe.
Many scientists reject the law of conservation of matter and energy and the principle of cause and effect - some even claim our universe came from nothing!
I might add that Genesis 1:1 is accurate in stating both heaven(s) and earth have a beginning.
Btw - Jehovah's Witnesses are not creationists - we reject some of their religious doctrines but we accept the Biblical account of creation.
Therefore, it is rational to reject your appeals to a realm you cannot define, cannot describe and cannot offer evidence for. Concluding that your asserted supernatural realms, agents, entities, etc., are non existent is perfectly rational