Westkoast,
Ray Allen's career average from 3-pt range is .396, just .004 from 40%!
This year he's shooting a little worse, just .358, but it is early in the season and he's with new teamates, so he's not getting quite the same shots as he used to.
And a three-pointer is more damaging to another team than a layup. Both plays really frustrate defenses - teams feel a little better about giving up a 3 pointer that a layup, but over time the 3 point shooter prevents your team from catching up.
Three pointers are devastating to a team that's trying to stay close or catch up. A team can make up for a layup by scoring on the other end. A 3 pointer means that you need one yourself to match it, and not all teams are proficient at making them.
No, Allen can't defend Parker, but Parker can't stay with Ray Allen either. Parker is not a great defender at the guard spot. He's not high on the list for steals. He's quick on offense, but not so fast on defense.