Yeah, I agree that it's not something that we should assume about all people. Of course, there are some trans* people who don't want to change their bodies, too... they feel like a man, for example, but they are happy to be a man in a body that looks female. There are as many versions of these experiences as there are people... like you gave an example above of feeling like you're not male or female, but you don't feel FTM.

(I feel like that would count as genderqueer or non-binary maybe?)

So I think really, we shouldn't assume that any person in the therian or otherkin community does or doesn't have dysphoria, and definitely we shouldn't use it as "criteria for being a therian". But I think we definitely need to acknowledge that it exists in some people in the community.

Whether it's a lot of people or not, shouldn't matter.