My opinion is that it's a fun theory, but it's really a gimmick. Way too many variables come into play when you talk about how pendulum sights are supposed to work for me to believe that it's anything more than luck, or the normal wide margin for error in archery/bowhunting. Pendulum sights, by design, result in a higher position of your bowsight if you're shooting uphill or downhill, does that make sense to anyone at all? No, it doesn't (if it does to you, then you REALLY need to go back to high school).
Practice is what's important for varied angle shots. Flatter shooting bows don't make up for everything, nor does any bowsight. Knowing where your rifle is going to hit before you release the arrow is what's important.