Thing is, the point guard will probably be the most important defensive position on this team. It is usually the position that is exposed most: everything runs through it. If he can't fight through screens and gets constantly burned, then he becomes another Jeff McInnis. Yes, we'll have a system, but a system requires everyone to do their job, and the PG's job is likely the most important. If he doesn't do his then we have troubles. We'd be the fastest, most exciting team in the NBA without a title. Sweet, but sorrowful.
At his point in his career, if he doesn't defend now, it's not likely that he'll learn. He has a big head and won't be happy sitting on the bench if his deficiencies show up.