The Keyblade and the Heartless

I'm not sure where it was even mentioned the Keyblade was the only weapon capable of defeating the heartless. All I remember is Leon mentioning that the heartless have a great fear of it. The only thing unique in killing heartless with a Keyblade is being able to release hearts (as shown in KH2 and 358/2 Days).

 

I assumed the reason was that it would be too much for Donald to Goofy to handle by themselves (especially when stronger Heartless were around harming others, as was the case in Land of the Dragons and Port Royal). I'm sure they could've fought the Heartless themselves, but without Sora's help, I doubt they would've lasted much longer.

 

Have you ever seen Donald and goofy fight? They kind of suck. They couldn't save the world's by themselves.

But yes keyblade release hearts and make sure they can't come back. Xion said whenever she killed a heartless without hers that they would pop up somewhere else. So they can be destroyed without but not completely wiped out. You would in a sense just be moving them out of one area into another.

 

But the difference is that Sora was helping them in those battles. She was only referring to what would happen if they fought battles without any help from Sora.

 

I believe you're thinking that what's shown in gameplay is indicative of what happens in the plot. To sum it up, what happens in gameplay doesn't really represent how it happens plot-wise, because gameplay can go however the player wants it to be (whether it be button mashing on the boss alone, or letting your allies do all the work while you stand in the corner doing nothing until it's time for the final blow). Just because you played a certain way doesn't mean that's how it happened. But when discussing the plot, I personally think it's safe to assume that Sora, Donald, Goofy, and whatever ally joins them contributes to battles equally. But back to the point, Sora is a very important part of the team, and the reality is, Donald and Goofy combined still can't be anywhere as strong as Sora (again, forget gameplay mechanics and whatever stats Donald and Goofy have). So, I still don't think having them fighting the Heartless without any help from Sora after the events of the 1000 Heartless battle would've been successful. Not at all. Besides, if Donald and Goofy could protect the worlds by themselves, then what was the point of them looking for Sora in the first place?