I was under the impression that the most useful comparisons are the parses from the same job and in the same instance, uploaded to fflogs for statistics and analysis. That wouldn't change whether the parser is showing your party members or not. If you are the only SMN in a Shinryu ex farm, seeing other people's dps is not going to tell you how well you are doing as a SMN. A 70th percentile RDM does slightly less damage than a 25th percentile SMN in Shinryu ex, so without knowing how other SMNs do you might think beating a RDM is an accomplishment. Whether the official parser was public or private it likely couldn't even be used to upload parses, so it would be better used for self-improvement.
Besides, once an official parser is implemented, what would stop us from comparing our numbers in /fc chat or a "Show your parse" thread? Voluntarily talking about numbers would not be forbidden anymore and it would be about as accurate as comparisons to random party members.
You just gave an example of how one would obtain context for their numbers in-game.