original-character-do-not-steal
Huh! I don't think that's a silly question at all, but it is interesting. They are both powers about convincing people of something different than what they were thinking or doing before.
Broadly speaking, I think that Agree to Agree and I Can Fix Them operate in different scopes. Agree to Agree is pretty narrowly focused on things like conversations and discussions where you're trying to find common ground or convince someone to come around to your viewpoint, while I Can Fix Them is aimed much more broadly and covers things like general patterns of behavior.
Another thing to consider is that the motivations behind the power are slightly different. This one's harder to explain, but…
I would say that Agree to Agree works best when you're working on a problem and can see a clear solution that, for whatever reason, nobody else around you seems to. In that situation, you could use Agree to Agree to get all your friends and allies on the same page so that you don't have to waste time arguing about the problem.
And then I Can Fix Them works best when there's someone who's doing things that hurt themselves and others because they're already hurting inside. I Can Fix Them lets you reach out to someone, fix their hurt, and show them a better way.
And while there's definitely overlap, they can't really stand in for each other. You could use Agree to Agree to convince someone that the way they're currently living their life isn't the best way they could be, but knowing that might not necessarily be enough for them to make a change. And you could use I Can Fix Them to try and get someone more invested in noticing and solving problems, but they might still disagree with you on what problems exist and how to solve them.
Did any of that help?