I would have loved this trade before the Nash signing. But I think a starting backcourt of two guys who are slightly undersized, slightly soft, and poor defenders would be problematic.
Nash is very good at staying infront of other PGs.
ESPN called him one of the underrated defenders before the season. Just because Dallas as a team couldn't play defense doesn't mean that Nash is a bad defender.
Ray Allen is definately not a good defender. Average at best.