D&D isn't a hobby?
But, yeah, there is an arbitrary distinction. The conclusion is that D&D has not been historically inclusive enough. To support this distinction against counterclaims, the definition of D&D has been narrowed to: only branded products, only iconic characters in those branded products, and only officially printed materials by the owner of the brand. You've kicked out all 3rd party supplements (of which Pathfinder certainly qualifies as a 3rd party supplement to 3.x), and dismissed characters on books (and why are novels allowed but not Pathfinder, again?) Because they're not sufficiently important enough, another arbitrary distinction. You're attempting to narrow the available material down until it fits your conclusion.
Which is a silly thing to do because, even if you include everything, it's pretty obvious that the arc over time is increasingly bending towards more inclusiveness, which is a good thing. This makes me think all of this "only branded D&D counts" stuff is less about making a point on inclusiveness and more about not being wrong on the internet.