Also, if you recall, the convention is the first time when most people start paying attention to the election anyway. And the exposure the candidates get in a prolonged primary is valuable face time to build comfort and recognizability. The primary offers far better media coverage than being on the campaign trail before the convention. And I believe Obama used his time on the primary campaign trail to build his state volunteers and organizations, which we should be doing as well. A long primary is wonderful for our election chances in every way (including vetting out negatives early) and more than offsets a delay at finalizing the nominee until the convention.
You are assuming a lot. A convention with floor fights, fractured positions on candidate platforms etc doesn’t go smoothly. The media will portray the Republican Party has being chaotic and unable to govern. Even the super-pacs can’t be going negative all the time. Whereas Obama will be trumpeting the end of the Afghan war, Iraq withdrawal, Osama bin Ladin’s capture; Auto Rescue Plan (they don’t call it a bail-out in Detroit); mortgage relief to 3m individuals, historical low interest rates etc etc., we would lack a defined candidate to speak for all and build his stature as what the public can view as a capable and competent WH occupant and speak to issues that show our candidate’s grasp of the major domestic and international issues of the day. Perception is everything politics. August is just too late for any of this.