If I understand it correctly PE is the most important rating for outside shooting. However, just having a really high perimeter rating won't mean the player is able to get an open look. For that he'll need speed and/or ball handling.
Alternatively, I feel that having a really good point guard can help get a less speedy/athletic player good looks.
I think athleticism plays into it when creating your own shot or getting to the rim.
I tend to think of a player with high perimeter but low athleticism/ball handling as someone like Jason Kapono or maybe John Paxson. Someone that primarily comes off screens to knock down outside shots. I'm not saying these guys aren't athletic, just not so much when compared to someone like D-Wade.
Conversely, someone with high athleticism, speed, and ball handling but low perimeter would be maybe Derrick Rose. great at driving to the basket but you don't necessarily want him shooting the three at the end of the game.
Put everything together and you might have someone like Jordan or Kobe.
So, in summary, I would think that you wouldn't want a back court of John Paxson and Kapono. Maybe one of these guys and then a more athletic guy like Rose. That way you have an outside option and a slasher. Hopefully your PG would be the slasher so he could set up easy looks for the perimeter player.
It's a long winded response but gives some insight into how I imagine things...