I think you're right in that symmetrical faces tend to be more attractive, and I have read some articles over the years about how this can subjectively determine how physically attractive a person is.
With your story, it seems like a classical example of good looks prevailing over the ugly. However, I would argue that sometimes looks can determine an individuals personality which can also determine a persons attraction quotient. For instance, an ugly person may not carry self confidence, or deliver refined social skills, they may be very introverted and be timid. A good looking person may come across very confident as well as being an extrovert. Something which may at first impression, stand out a little more.
Of course, in some of my other Miss Opinionated series, I have discussed the qualities of nice guys but with boring personalities vs the 'bad' guys who give women a sense of excitement. These traits cannot be overlooked as I believe they are inextricably linked with your perception of your own attractiveness. The more attractive you are, the more you give off the air of being a 'bad' guy etc.
As for changing norms and the shift to good looking women being with regular looking men, I think the explanation that seems obvious is that women are less interested in visual attraction. Aesthetics contribute a part of the attraction, but not all. More important is perhaps the ability for the male to provide security. A man who is unable to score with women on looks alone will likely appreciate and stick with their mate as opposed to a good looking man who may be fickle and attempt to mate with many partners.
(I'm trying really hard to not introduce the idea of money but clearly this factor invariably plays a role too.)
Indeed, very good points. As you say I think security is a factor also ans of course a confident personality helps. Still it all comes across as a kind of mating "game, however we analyse it. And in every game there are always winners and losers and so far those who have symmetrical faces have a distinct advantage over those who do not.