Most people do denigrate their exes, and it's highly unlikely that all their exes have been two standard deviations away from the mean (for that quality) while

Most people do denigrate their exes, and it's highly unlikely that all their exes have been two standard deviations away from the mean (for that quality) while their current partner is at the mean. Much more likely, if you have a partner who is great at playing the piano (or at politics, or whatever) but all your previous partners have not been, most likely the average person just isn't great at playing the piano. In other words, if you're saying nice things about your partner, the implication is that it's not generally true of other people of their gender - whether or not you spell it out.