I agree, that would be interesting to present - perhaps as an outward facing post for investors.
I think @pharesim / @curangel did just that a month or two back for their project.
It's something anyone could do I guess. Lease to curie, and delegate the same amounts to curangel, ocdb, (edit: and qurator!), and see how the ROI compares.
It could be that delegators want to focus on particular content (I don't think the above projects do other than 'not Hive'), and so they could 'lose' a little ROI but see more of the content they like.
The content does indeed play a role and these projects do need to be open with what kind of content they upvote. Could be interesting to see purely from an investors standpoint. Always fun to see the stats.