I am not trying to put anyone down, it's just that dressage riders have learned a lot more communication with the horse and they would obviously need a bit a practice.
Now this is what I'm thinking: If you take a classical dressage rider(very few out there) and ask them to do modern dressage movements, it would be a piece of cake for them. In modern dressage these days, I see a lot of short cuts, contraptions, heavy hands, horses heavy on the forehand, etc. They can do piaffe(much better than modern riders), passage, pirouettes, extension just as well or better. They communicate better, use their seat more, and right with light hands. I am not saying that modern dressage riders are bad, they just ride differently(I ride dressage myself). But many riders these days just don't care about the horse, they care about winning and they care about their own ego. The sell their horse for a better horse, like they are riding machines.
*I am not putting labels on all riders.
Here are classical pictures:
And modern dressage pictures
There are lots of good modern riders:
And what makes a classical rider different from a modern rider?