The long axis of the creature's torso, for example, is angled downwards at about 45 degrees. Now, there is nothing wrong with this per se, but then the neck of the creature is angled upwards at 45 degrees. The two meet at too acute an angle and this I find a little jarring. I think that a slightly less acute angle here, with the neck not sticking upwards but more horizontally, would create a better impression. The overall impression is of a V-shape and I think this may account partly for the perception of the figure being 'mangled'. The overall impression here is not just one of dynamism, but of hyper-dynamism. Similarly, the sorceress' is looking upwards, and her spear is also aimed upwards. Again this forms a very angular impression. Of course a rider can conceivably hold a spear or staff in any position, but I am not criticising the figure in terms of being unrealistic, but only expressing an opinion about the form of this sculpt.
Now, I will not get into any debates about whether or not it is "realistic" for a flying horse to be depicted this way, because of course it is for the individual artist to choose how exactly a mythical creature in a magical universe should look. But I do think that a less angular look, with the figure not having these acute angles would give a smoother, less disjointed impression.
So de gustibus non disputandum and all that sort of thing, but I do hope that RH will use the comments on this thread positively and come up with a smoother, sleeker final version.