I've seen something like this brought up before. As with last time, I can give a unique viewpoint regarding merchandise, as I live close to Walt Disney World (and several Disney stores in places like malls and the airport) and so I get to see the current merchandising situation dozens of times a year.
All of those princesses are mostly equal in their popularity if you go by store shelf space, except for Jasmine (she's actually a bit uncommon) and Pocahontas (since her movie didn't do as well as all the others). There's also Merida from Brave, and Elsa and Anna from Frozen are very rapidly appearing; there's even a rumor that the Maelstrom ride at Epcot's Norway pavilion will be remade into a Frozen attraction. I wouldn't complain.
What you can also look at is the appearances of actresses as the different characters in the parks. Belle, Snow White, Ariel, Cinderella, and Sleeping Beauty are the most popular (though this is likely a grandfather clause kind of thing keeping all of them so visible), with Elsa and Anna, again, making a prominent and nearly permanent appearance in the Norway pavilion. Jasmine and Aladdin show up regularly at the Morocco pavilion, and you can reliably find them there. Merida is still rare, and Mulan is uncommonly seen at the China pavilion. Pocahontas is almost never seen, again likely due to the movie being a bit less popular than all the others. Tiana is occasionally seen at the Magic Kingdom, near Liberty Square.
However, this isn't really due to intentional racism as much as it is actress availability. Disney has very exacting standards regarding appearance, including height, for every single one of their face characters. Belle, Snow White, Ariel, Cinderella, and Sleeping Beauty are all the easiest to cast because Florida is pretty much overflowing with Caucasian female actresses. Jasmine and Aladdin are usually just olive-skinned Caucasians, and most people don't notice the difference unless they're eyeing skin color of all the actors to judge them. But for ethnic characters, you need actresses who are at least close to the right ethnicity (most normal people wouldn't complain if a Japanese woman was cast as Mulan) AND look the part. Florida is predominately white, followed by Hispanic and black. If you're wanting to cast a Mulan, you've got less than 2.1% of the population who MIGHT look the part and are the right height and have the acting talent (people always forget about acting talent; someone who looks like a clone of Pocahontas is useless if she can't actually do the job).
