I didn't say development I said his story was continued. Also I think it's very much in character to do what he considers the heroic and right thing to do aka supporting Cap who asked for help. I'll eloberate that further below. In any case: His story continues, that has nothing to do with personality traits.
I don't think it ruins it at all, it just gives us a different starting point for Ant Man and the Wasp coming in 20-something.
Also after the whole Infinity War they won't be able but to pardon him and throw the accords outta the window anyway. That is if he survives.
Look at it from this angle: If Cap asks you for help and you think he is on the right, what would it say about Scott to deny him his help?
Sure he could have said he wants to be able to spend time with his daughter but it just wouldn't feel in character for him to use that as a reason to "bail".
He wants to be a Hero for her and that is what a Hero does.
@All: I doubt the ending of Civil War means that the Avengers can be best buddies again just like that. Sure Cap made a first step but these guys won't go out drinking beer together any time soon. I even think both teams will be defeated during the next Movie before they realize they can only do that together.