I've seen some really strange results from the zone defenses. In one of the games this season, I played LI against a 2-3 and my center went 13-14 (only miss was last second 3) so he was 13-13 on the inside against a more expensive center. The team I was playing against had a good inside defense rating as well. Maybe his center just wasn't enough even with the added zone. I noticed more alley oops and I wonder if the decreased outside defense allows the perimeter players to move the ball better- leading to more easy buckets. In addition, I read a post stating that the 2-3 zone increases defense on the inside but doesn't help against what he called 'close shots' regarding results from running his game analyzer. Making the argument that it is not worth giving up so much outside defense to only increase some defense inside without having an advantage on close shots.
Here is a link to the game if you are curious
http://www.buzzerbeater.com/match/32858261/boxscore.aspx