I wonder if data taken from other sites (such as ao3) would produce similar or different results for numbers of works tagged. Ffnet doesn't have the most useful pairing tags.

I don't think this necessarily means the most shipped with either. I looked out of interest and found 198 pages of works for harry/voldemort so that's a) a very high amount of favourites for a smaller number of works but b) a much smaller number of works published total than say Harry/Herminione (2.2k pages) or Draco (3.6k pages).

e: I was curious so looking at ff.net filtered to [Harry P/Hermione G.] has a total 12000~ favourites shown on one page of fanfiction alone. The data here is definitely a bit wonky.