For most of the books, Harry can't pull of a decent veil to save his own ass. That still doesn't mean that spirit evocations are incapable of creating veils, which is a question more comparable to the content of this debate.
He also doesn't use air to move things around, even though that's one of it's strong suits. That's not how his training has air working for him, not how he conceptualizes it. He uses spirit. Further, where veils are something that Harry is just not good at, he has specifically that healing is extremely difficult and delicate. Even Elaine, who is quite a bit better at delicate magic than Harry, can only heal minor injuries and that's with a ritual/thamaturgy application, not evocation.
Devonapple, I really like the black box description.
With the Aspect discussion, where do you draw the line though between someone not being able to generate an effect though and simply something that you're a lot better at because you have an Aspect that you can Invoke? I can definitely see the benefits of requiring an Aspect, and having one would definitely help solve a debate on it. On the other hand it also seems like something that with a character with thought about heritage for your spellcasting framework would really not need an Aspect.