"More popular" has to equal something other than "my real life friends like *****Man more".
Sales is a good measure. For these companies, they don't care is Spider is more popular than Bats... they care if Spider SELLS more than Bats. Even if people were buying the Spiderman merch just to let it float in their toilet and poop on it, the companies would consider that success.
Now if you are comparing to "popular" to "critically acclaimed" then maybe you can say that sales is something to minimize since "critically acclaimed" is subjective.
If the merch sales doesn't make Spidey more popular, then you need to come with some numbers of another sort that show someone else being more popular - not just "me and my friends like like the G**damned Batman".