It seems like joining the Whitebeards crew back then was a disservice to Ace. He wasn't anymore his own man after that, serving under somebody as big as Whitebeard. He lost his own drive. Luffy was a captain from the beginning and thus lives for his own ideals and motivations. Based on this episode Ace is happier following Whitebeard to death than continuing on his own. I guess Whitebeard didn't predict this.