The only problem with McCain's assessment is the usual one:
There is no way to know what outcomes would have resulted from different tactics. Things might have gone better, or might have gone worse. Even with the benefit of hindsight, we cannot be certain of alternate outcomes.
For example, more troops might have totally turned off the Iraqi citizens, and they might not have turned out to vote, and might have joined the insurgency in greater numbers.
None of this matters now. Just like our own lives, we learn, adjust, move forward and succeed.
Or not.
Whether we think we can succeed, or think we can't, we are correct.
There should never have been a vote before pacification was achieved. It was a gimmick to justify the war. A military governor was needed to hold the place together until some semblance of order was achieved.