1. "Effect".
2. Huh? Is your point that a guard has to run the offense and that's a bigger part of the offense than him merely guarding perimeter players is a part of the defense?
If so, well, first, that's only true of traditional PGs. So the classic case that supports your view would be Steve Nash - he was everything to the offense but also a very mediocre defender. But, despite Nash winning back-to-back MVPs, he never made it to the Finals. And his role in the offense was more than almost any other PG. Some teams make do without a trad. PG at all, most notably Jordan's Bulls because of the Triangle. And that's probably better, because it involves everybody and makes the offense much harder to guard. So, actually, it's probably not a good idea if your PG _is_ super important to your offense. Chris Paul is even a good defender, but his team's failures in the playoffs are well-known. Curry is a much less traditional PG, and the ball-movement in that team is what makes it great, not him hogging the ball.