I'm thinking more along the lines of Iroh Jr. being
the Ace. I think his presence will be important in stopping Amon, but I have no expectations for what happens in the battle of the city since it just seems like it can go either way really really easily. I think we'll be seeing that Iroh Jr. is damn good at whatever he does when he's onscreen, but ultimately only steals the spotlight briefly and Korra's gang still does the real dramatic stuff(kinda like all the folks that helped defeat the Fire Nation armies rather than Azula the Firelord himself in Avatar's final season, only with a more unstoppable badass vibe to it).
I figure they're setting up Amon to be defeated and to be replaced with an even more threatening antagonist or like when the solar eclipse wasn't enough to defeat the Fire Nation in Avatar, letting him have his way in the season finale while Korra's gang runs off to train and kick his ass.