Perspective in definitions is a no go. When someone says that an app is not professional, due to the definition of a professional app, he means that no professional work can be done on this app. Or at least that's what I understand from it.
If they clarify further that what they mean is, it's not suitable for their professional work, I have nothing against that. But they don't and their wording exactly means that "this is not for ANY professional out there". Nobody seems to make their argument personal and generalize immediately.
About your analogy, I'd say it's not the poorest analogy I've seen but if you consider the functions, I'd say it's poor. You cannot use the car you described as a race car. In addition to that, no race driver can use that as a race car.
But FCPX as it stands today can be used by "some" professionals to do their work. I hope we agree on this.
I agree, I don't see why a professional plumber couldn't make a promo video with this.
As for film/Advertising, no, you can't work without XML/EDL options.