It's incredibly dismissive of the other princesses, especially because even the most romantic movies is not "women is worthless without her man" even in Cinderella her goal wasn't to marry a prince but to have a chance to get away from her hard life for just one night.
I understand them being thin but that's more about them looking the the characters (even Merida is thin).
Having weapons doesn't necessarily make a character capable or not. It's how they use them and Princesses like Merida and Mulan might wield a sword and bow and be amazing at it, but other characters like Snow White, their greatest super power is their quiet strength, just look at how she takes no nonsense from the dwarves when they try to get away eating with dirty hands.
I am not saying it's bad to have warrior women without a love interest. I also love Merida and her movie. However I don't at all like saying the other princesses are weak and sexist in comparison because they aren't.