#2 The boss shouldn't win

This point is subjective and depends on how one looks at it. While Kenny Omega is a top wrestler and believable to win the match, he is also an Executive Vice President of the company.
WCW is the most prominent example of what happens when the wrestlers get creative control, and AEW promised to learn from their mistakes.
Top name doesn't want to enter the WWE Hall of Fame. More details HERE.
It could pass on as a one-off match, and it would be fine with everyone if Kenny Omega wins, but the promotion could send out a message from their first show that they won't commit the same mistakes.
Kenny Omega is a bona fide wrestler and could afford to take a loss for the greater good. It doesn't mean that he loses every match. It's more about sending a message about their intentions, and Double or Nothing is the best platform for it.
#1 Gives momentum to Jericho for his upcoming fight against Kazuchika Okada
Chris Jericho is scheduled to face the IWGP Heavyweight Champion Kazuchika Okada at NJPW Dominion. The contest is a dream match between the two superstars in just a couple of weeks after Double or Nothing.
As AEW claimed on various occasions, wins and losses will matter under their promotion and even outside their company. For a similar reason, Adam Page and PAC's match got canceled.
A win over Kenny Omega provides an enormous boost to his momentum, and even if he loses his match at Dominion, a presumably 4+ star match doesn't bring down his credibility. Similarly, Kenny won't lose much momentum if he takes the loss.
There could be an argument that if Jericho loses to Okada, he won't be a great choice to become AEW's top champion. But there's always a chance that the winner of the Casino Battle Royal wins the championship.