Obama campaign manager David Plouffe reflects in an interview:

We went through as rigorous a primary as we’ve ever seen in our country’s history, I think, and there’s no doubt that made us a stronger general election candidate. A lot of our dirty laundry was aired, and we had practice in testing a campaign. Clinton, she was formidable, the campaign was formidable, it was very aggressive. We were the front-runner for a while, which meant the press took a bite out of us. We had really been tested, and we went into the general election in very much fighting shape. We were ready for those five months because we had been through 54 primaries and caucuses, and run the gauntlet. McCain hadn’t done that. For all of his years in public life, he never went through anything like what we did in that primary.

This is an argument I entertained back in July. At the time, it was dismissed by RSM, who was still PUMA-struck.