Well, the thing about the Q is that according to some accounts they are all smoke and mirrors. Not nearly as omnipotent or powerful as they like to make themselves out to be.
That would have been a far superior way to present the Q in future interactions, and wouldn't have contradicted anything we saw in TNG.
They're pretty powerful, but not omnipotent. The fact that they couldn't control each other (or force humans/others to bend to their will) proves that they're not omnipotent.