I don't know anything about Ness and Kirby.
But don't all of these characters need power ups to do anything?
I thought Rosalina needed the power of the stars/lumas to do anything. That is where the true power lies. She just happened to meet the Lumas and learned how things worked in Mario's Galaxy, I guess. I need to read her story book again.
Pit had the treasures and Palutena's power of flight power ups to take down Hades and co.
Shulk has the Monado that only he can wield without issues (see Dunban, the former wielder in that game).
Ike had another Goddess help him defeat one just like Pit.
All these characters are servants to greater beings. They're just chosen to take up a large cause.
Kid Icarus' "deities" were slayed by each other
, by Aliens, or by special divine weapons that Pit would wield. All through out that game, the supposed almighty beings were powerful, but quite fragile.