DMI is intentionally designed to massively exaggerate the effect of game shape. So in general, equal DMI doesn't mean equal performance in any respect.
3) As for your last question: I find it to be completely dependent on the circumstances, opponents' tactics, tendendencies (e.g. what do they play at SF? more important to protect the perimeter or to protect the paint and rebound?)
2) on this basis I am tempted to say that player A would defend and pass better than player A, but do all other things worse. This is not one of your question, but I think it's about right.
No, of course not. But since Player's A two skills at Prominent take bigger share of his DMI than rest of his skills, we can say that compared to Player B, Player's A relative skills look like this:6, 68, 66, 86, 66, 6
But player A's game shape isn't horrible (it's respectable), so it's more that player B would be getting a performance boost rather than player A getting a penalty. Perhaps player B now has all skills close to 8? While player A has has all 7s except the 10s in PA & OD.