As stellar as Ibaka was playing, Perkins was the opposite (likely due to injury). I think if you take an average night between both of their games, the Bulls have no answer in the front court for a team that has Perkins, Ibaka, Durant, and Collison (VERY underrated). They don't have the depth to prevent productivity (offensively and defensively) of those players with Asik gone - and that is the strength of the Bulls. The only way the Bulls 'caught up' to a team like the Thunder is because of the Harden trade (though Martin is still very effective).
Perhaps, perhaps not. I still think a healthy Bulls team can beat a healthy OKC team in a 7-game series. Let's hope we get to see that and i'm proven right