You are describing the conformation, and sought after conformation, of the American Quarter Horse.
This is, in slight variation, the most sought after and successful build for both reining stockhorse work, and actual cattle handling, as we see in Cutting Horse competition, and Penning, as well as roping events.
On the contrary, when you have a horse that seems disproportionately powerful behind and a bit less so in front you have great mobility of the forehand. If you google up "reining horse," and point to YouTube you can find many instances of videos of these horses doing almost miraculous movement over the haunches with quick and powerful forehand agility.
Compare, for instance, the American gaited breeds, the Saddlebred, the Tennesee Walker, and others, they are the opposite...very uphill with a feeling of a lot of horse in front of you when ridden. They are not well suited to some activities but very much so for others - that require more power over the forehand. I would not do cattle cutting with one, nor reining work.
The eventing horse is the horse that we think of as the most balanced end to end I believe. Our Warmbloods in all the variations. Probably the horse conformation most closely adhering to balance between forehand and hindquarters is the dressage horse, and Thoroughbred.
Continue to train your eye as you are doing. Your descriptions are very clear and quite accurate.
I rode QHs for many years, as well as TBs. Each had wonderful things to offer and wonderful potentials to develop. The first Spanish horse I rode, later in life, told me very clearly where the QH had come from, as the movement, at least for the more baroque physique Iberian horses, and the QH are extremely close.
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