I suppose the one upside of DL not offering Comfort+ on aircraft with Premium Select is that people won't book W class (the almost near universal fare basis for premium economy on other airlines, including on most of DL's partners) and think they are getting real premium economy.
I honestly don't think anybody with enough knowledge about flying to understand Y/W/J/F, especially with W being the most obscure of those codes, would buy a C+ fare thinking it was Premium Economy, especially with how Delta's website now very clearly places the Premium Economy option to the right of C+, even when it's not available on a given flight.