I think it's overstated. I think it's hard for any single one feature to ruin someone's looks unless it's devastatingly bad. You can find loads of good looking people with a weak chin, or bad nose, or a long phultrum.George Clooney's philtrum always looked a bit on the long side to me.
This is a good insight. I hadn't looked at it that way.
The most important aspect of it is the nose:upper lip ratio. Other important factors influencing perception of philtrum size are philtrum curvature, maxillary rotation and projection and nasolabial angle.
This is true. My lefort I advancement did not change the length of the lip (that's impossible), but because it's now vertical and closer to the viewer it looks longer.