I personally don't like the idea that the Celestials were responsible for the Big Bang, and thus the Infinity Stones.
In my mind, it begs the question why didn't Arishem stop Thanos? Tiamut's Emergence and countless others were delayed by the Snap.
Also, I have a theory about Tiamut's Emergence. I just got done rewatching A.o.S. season 5. I think Glenn Talbot aka Graviton was successful in stoping Thanos. Ajak would have never had a change of heart and the Eternals would have never stopped Tiamut's Emergence. Earth would have been shattered as a result of the Emergence rather than Graviton accidentally destroying the Earth.