^As I said, I'm not intrinsically against updating, but that doesn't mean I consider every given update to be an improvement. An update can be good or bad; quality can only be assessed case by case, not by category.
Maybe it's because I'm fashion-illiterate, but I just don't see why the trunks are so much more objectionable than any other part of the costume. To me they're just part of Superman's look. Maybe it's just that the "underwear on the outside" joke became a pervasive meme and convinced people to fixate on the trunks as a symbol of comic-book hokiness. If the pundits and wags had chosen to make a running joke out of the cape or the color scheme instead, then that's what would be getting phased out today. Fashion is more about conformity to group opinion than any objective standard of aesthetics or practicality.