It's partly speculations and assumptions, but not completely.
The part about 3pt shooting % is actually based on extensive statistical analysis that was shared on the forum some time ago. If I recall correctly, it was contributed by Lemonshine. (If I am mistaken, my apologies to all concerned.)
The part about custom player designs and team ratings comes partly from my personal experience, since I had a couple of players who were designed in such a way (to switch the positions in attack and defense), be it for the sake of research or experiment or to save on salaries (this way, you can have some very powerful builds for around 80k). And I noticed the depressing effect on ratings, even if such player was not lacking in attack (as a PG, for instance) or on the defensive end (as a PF/C in this case). Actually, team ratings were better when he played on his projected position (by GE) on both ends of the floor, even if his attacking (or defending) skills were much more suitable for some other position.
Do you know how important passing is for PF/C, from what I understand they don't contribute to team's flow ranking?
Maybe they don't contribute to flow rating (which value/effect is hard to define, as we can see), but that doesn't mean they are not important.
So in your experience swapping positions etc didn't work for overall result even the skills were more suitable for swapping?
So the question remains here, how passing helps PF/C to play better?