I'm seeing a whole lot of speculation here and a whole lot of supposition.
Not once in the issue is omniverse mentioned. The universe is mentioned both on panel and on the marvel site you keep directing us to.
Once again, whilst 616 is the prime universe from which all the others originate, the other alternate realities within Marvel creation are NOT created all at once with a single Big Bang.
If that was the case you would not have universe within Marvel which are yet to go through their Big Bang as seen in Ultimate F4. All universes would be the same age if they were all created at once.
Alternate realities are created through things such as alteration of events via time travel/manipulation, as demonstrated in Here Comes Tomorrow or Age of Apocalypse. Those realities never existed all along, they were the result of tamperings with events in the 616 timeline.
You cannot try and make someones feat seem more powerful than it is by saying that one Big Bang directly resulted in all of creation. Other realities formed from the prime one as time went on.