Sadly, it was just a disjointed mess. Even if McGovern had given that speech at a reasonable time, he was still going to lose in a landslide. McGovern was a great guy, a great senator, but easily defined and because of that, he could never shake being the candidate of amnesty, abortion and acid. The Eagleton disaster didn't help endear him to Americans, either.
It was just a poorly run campaign. The only way McGovern had a shot at victory in '72 is if Watergate blew up during the election and even then, I'm not so sure he would've won. It's just one of those elections, like in '84 and '96, where the incumbent is almost certainly unbeatable.