Shoulder / hip / heel alignment is meant for dressage and western pleasure, both of which mean highly trained horses riding in an arena and covering the ground slowly, with lots of collection. That isn't the same as endurance riding, roping, etc.
Here's a photo of my dad roping, even though his body is turned to look behind him like it should be when pulling a steer, his leg didn't shoot forward or backward, he kept it where it should be.
I guess what I'm saying is that, yes, when we do things that aren't just "flatwork" (call it what you will) our positions change to make the task at hand easier, but I think it should be a goal to always push for being as close to the ideal shoulder/hip/heel alignment as possible. That position should be a solid base before any other style influences it.
Even in these video stills, you can see that I still have my position pretty balanced, my leg hasn't gotten away from me and I can still be an effective rider, and it wouldn't take much to get back to that ideal shoulder/hip/heel alignment if I wanted to.