Unfortunately, I think you are realizing that not all of the artists are created the same. Some are just better at rigging than others, not to mention the whole issue of "did they include the morphs I really need." (Another rant for another day.) 

As to changing the xyz at the hip, I believe you'll find that quite effective. I agree that changing other body parts is not a good idea, but since there are no movement morphs associated with the hip, I believe you'll find it an effective positioning tool, if it's available.

And yes, you are going to have to learn the setup room to reconsile some issues.

One other thought...

In the case of the saddle, could you not position it as you desire, then set the parent figure to the horse, instead of conforming it? It might not be quite as convenient in extreme poses, but ought to at least let you get the effect you want.