Worst Case Scenario
Dean Ambrose cannot simply beat Brock Lesnar. Brock Lesnar is the man who has beaten everyone, including The Undertaker… in the match that ended the dead man’s streak. Even with all the weapons he’s inherited, and the support of some legendary lunatics… David should not be able to topple Goliath.
If Ambrose beats Lesnar, there’s no excuse for him not to beat Triple H, or Roman Reigns, or Seth Rollins, or whoever else may happen to win the WWE World Heavyweight Championship. There’s no reason for Ambrose not to immediately become the guy.
Dean Ambrose should become the guy… but it should happen with time. A win here means you need to move forward, and fast… or else Ambrose will get lost in the fold.