While what you say is very good reasoning and brings validity to the conversation I must say I think we give hitters to much credit sometimes... In my experience most hitters aren't good enough to hit it at a certain hole with Much consistency or effectively enough to warrant any kind of movement by the pitcher falling to one side or the other. Although a good pitcher knows how to fill a hole I tend to think stepping back and setting up for a ball to come right at you does just as good as falling to the hole your 5 man is not.
I always fall to the side my 5 man is not on because I will never set up right behind the rubber. Seen too many bad hops off the rubber, and have even seen a few guys trip over it.
The 6 hole is the only one I feel is a big gimmie after middle. It's pull, where most of us hit if we came over from baseball, etc. If your SS isn't playing more towards third with a 5 man it's basically just trying to cover middle.
Similarly, I've played with several 2B that shade the middle in a 5 man and leave a huge 4 hole. I've never understood that. Especially when I'm falling that way.