I agree with you that these attractions (along with characters such as Figment and the Country Bears) became IPs the moment they were created, but this doesn't undermine what those opposed to the use of preexisting IPs are saying. On the contrary, it supports their argument that original ideas developed for the parks take on a life and significance of their own, greatly contributing to what makes WDW (and the other Disney resorts) special and distinctive.
I personally think of these "park IPs" (if I can call them that) as foundational, by which I mean they are essential to the parks but also sufficiently present as a sort of underpinning that the addition of preexisting IPs is not in itself detrimental. For my part, I enjoy seeing the films and characters I love brought to life, but then I've always been clear about the fact that I'm more of a Disney person than I am a theme-park person.