I think its good to put beginner riders on advanced horses.
Do you ever go to a riding school (not all) and notice how all the beginner horses are completely dead to leg and rein commands? That's because all the beginner riders kick and pull, because that's all the horses will respond to. That means these riders are being trained to kick and have heavy hands.
Put them on an advanced horse and they can learn subtle aids. They can learn what collection feels like. They can learn more advanced movements and begin to understand the subtleties of what is being taught.
This horse might be a bit of a handful, but if it wasn't calm and safe in an arena I seriously doubt an instructor would put someone on it. It would be a very stupid move.
I'd just like to point out, most of the time the reason why beginner horses are so dead to leg and rein is because of the beginner riders
. When they are just learning to ride, they don't understand what the heck subtlety is. They don't know how it feels and they don't know how to use subtle aids. And they aren't going to learn it in the snap of your fingers, because most importantly they can't
use subtle aids. It takes balance and muscle memory to do that
, and when a beginner starts out they don't have either. Nope, when a beginner rider starts out they are going to be all over the place and just plain messy. Those subtle aids will just confuse the horse.
So in the mean time until they learn muscle memory and balance and gain experience, they are usually put on a beginner horse. Most beginner horses are quiet, safe, and yes, a little dead to leg and rein. That's simply because they are used to beginner riders pulling and kicking and doing god knows what on their backs. No matter what, no matter how great an instructor this beginner has, it's inevitable that they will make a million mistakes while learning to ride. The horse has to be forgiving and put up with that. But if you put a beginner rider on an advanced horse, think of how potentially dangerous that would be. Advanced horses are advanced for a reason: because beginners don't have the experience, muscle memory, or balance to ride them effectively. Often they will respond to the slightest of cues, and just think of how many mixed signals the beginner will be giving.
Remember, time is the greatest teacher.