think about Tony Parker and Nate Robinson..both of them can drive the ball well but only one of them can finish very hard lay-ups..driving gives the player better opportunities for a shot, which means better percentage but it is nothing without IS and JS skills..
IS matters for the guards but so does ID..you don't have to train it because there are not many guards with good ID skills..if you play "look inside" or "low post", your guards will get inside many times..zone defense does not change anything, still PG defends PG, SG defends SG..