In general what you say is true. But "the Sunnis" weren't our enemy. The Baathists--supporters of Saddam, were, you can say. But not even all of them are enemies--some just joined "the Party" in order to be employed. High-ranking Baathists are the ones we oppose. And they have been purged--but so have all the lower-ranking people--which means a large number of people are being blackballed for employment. That's one of the--many--issues which the Maliki government is to take care of. But it's not likely any time soon.
Nor is anything else--except the gradual dissolution of Iraq. Starting with "Kurdistan", which never wanted to be part of Iraq in the first place--and including Kirkuk and its oil. Then southern Iraq, mostly Shia, and seeing "Kurdistan" as a good model. So what will Maliki--or his successor actually rule?
And this will happen regardless of anything we do.
So the US will wind up in "Kurdistan"--which is fine with the Kurds, since it will deter possible rash Turkish moves--like a full-scale invasion to stamp out the PKK, the Kurdish rebels--based both in Turkey and Iraq--who have in fact killed quite a few in Turkey.
So the only question is the timeline for this--how long it will take.