2-3 doesn't lower the % of the bigs, every pass they receive seems to set them up well but they rarely get the ball as if passing lanes are blocked. This is regardless of the orientation in offense. There are too many open shots from close range as moutlinho has shown. And there is a small imbalance i think in the way the GE evaluate shooting opportunities against a 2-3 zone.
It means that what makes for the inside defense rating in 2-3 is useless. The GE will simply ignore chances in the paint and 2-3 won't even be able to stop the few oportunities of the opponent's C. If he is not well assisted, it should be harder for him to score. It is the least this zone should do, to prevent easy buckets by the opponent's C.