Sometimes I think they should have an IDPA approach to classification, if you rank high enough at a major you should bump. If you go to nationals and beat 50 B's, I would say you are not a B. Giving you your percentage of the winner at a major like they do now generally makes people's scores go down.
In the end I think it's helpful to look at classification and match performance as two separate things. Maybe with the new classifiers incorporating movement it'll change, but I think if you really want to move up you have to practice classifiers or classifier-ish drills.
I will say though, that in general, match performance and class do seem to correlate pretty well. When you look at majors the results do (pretty much) go in order.