fandoms, regardless of size, tend to have the exact same pattern in terms of ship popularity
what do I mean?
if you go on AO3, and go into the tag for a certain fandom (for instance, the Silmarillion), you can go to the filter bar on the right and use it to see the ten most popular ships and how many fics are tagged for those ships
so I pulled the numbers of fics and the rankings and graphed them against each other for a bunch of fandoms
they all have the exact same shape:
they all look like this, without exception
(I find it highly likely that this form would break down for very small fandoms with under 100-200 fics. Not sure what the cutoff is, haven’t tested)
now what’s cool, is they all really really nicely fit a certain equation form: y = Cx^-n, where C relates to the total number of fics written (i.e. roughly equivalent to fandom size) and n is an index that determines how “steep” the drop-off is on the curve. For instance, in fandoms where the top ship vastly outnumbers any other ship (by say, 10 to 1), n is a large number. (well, it’s always negative, so it’s a large negative number but point still stands). Where there’s a relatively more even distribution, n is small. n for the Silm is actually relatively small compared to most of the fandoms I’ve looked at.
the highest n value I found was for the Torchwood fandom, at 1.64. This is because the canon ship Janto dwarfs basically everything else by a huge margin. Lowest was for Marvel, at 0.801. Edit: new lowest is LotR, at 0.568.
Fandom size does not appear to be correlated to n value, which is interesting.
If anyone wants to know what a specific fandom’s shipping pattern looks like let me know!