I do like the fact that the background of the image is pretty uncluttered, as it allows the viewer to focus on the action in front of them. I know you used a 200mm lens, but the way that brings the viewer close to the action and almost makes them feel like they're about to get ridden over is great
I think the image, as it currently stands is okay but maybe a little boring? (Sorry!) It's not easy to photograph horses jumping straight on, as often you won't get a straight on view (as is the case here, it's slightly off so you're looking down the body of the horse as well). Although this can
work, I think it needs to be either more so in this case or not there at all. I think too, that a straight on view would work better with a much higher fence, so that the viewer can really see the power and effort the horse (and rider, of course!) puts into getting lift off and getting over it.
Bright white bits on the wings of the fence are, as you describe, a nightmare in bright sunlit conditions but to be fair you've done really well here to keep them from blowing out completely. The grass is green, the sky is blue and the horse's feet are all up off the ground (bar one slightly lazy back leg
I'm not going to suggest anything more post processing wise with this image, as I think it's been covered above, but maybe give you some things to think about for next time. Looking in your portfolio, you've got a few cross-country and show jumping images and I think there's a couple in there that are more successful than this one (Freedom and Freedom 2 are obvious choices for me).
One of the beautiful things about watching horses perform is the 'shape' they make in the air as they go over a jump (known as 'bascule') and I think sometimes that getting a side-on angle is more pleasing as it allows both the jump and the horse to been seen in all their glory.
Another thing to maybe think about next time is the creative side of photographing show jumping (or cross country) and use a panning technique to capture the horses as they approach, take, and then move away from a jump or obstacle. You'd have to time pressing the shutter, or pre-focus on the jump itself, but that kind of technique can produce some beautiful images which are much more about power and movement, and less about a static moment in time.
Although it's an old thread, you may find this
interesting reading. It's a short thread, and may go over what you already know, but it also might give you some other ideas as well
(And if I sound really enthusiastic about this kind of imagery, I used to do show jumping and eventing as well as dressage, so the beauty and power of horses and what they're capable of really does resonate with me