How reasonable? I think pretty reasonable; MoR directly criticizes canon on numerous occasions, from the exchange rate to Hermione being Sorted into Gryffindor to Harry using random curses on Slytherins and on and on. Reading through one link on that, I see nothing about the Seuss parody parodizing Seuss, and plenty that fits MoR, eg.:

Parody achieves its status as social commentary by disparaging the original work, however slightly, by "pointing out faults, revealing hidden affectations, emphasizing weaknesses, and diminishing strengths.^1^

or

The court concluded that the infringing work broadly mimicked Dr. Seuss' characteristic style, but it did not ridicule that style. 170 The court noted that Penguin's use of the Cat's stove-pipe hat, Dr. Juice as a narrator, and a title similar to the original's title were all means of drawing attention to the new work, perhaps "to avoid the drudgery in working up something fresh."171

Finally, with regard to the purpose and character of use, the Ninth Circuit considered whether The Cat NOT in the Hat! merely superseded the Dr. Seuss originals or whether it "transformed" those works. 172 The court did not recognize any effort to create a transformative work. 173 As a result, under the first factor, the court concluded the scale tipped against fair use because the infringing work was neither a parody nor transformative. I74

...When considering a parodist's claim to fair use, a court must first determine if an infringer's work meets the threshold requirement for the defense: "whether a parodic character may reasonably be perceived. >7232 Courts have recognized parody as a work containing a discernible direct comment on the original. 233 Although the Ninth Circuit conceded Penguin's work did broadly mimic Dr. Seuss' style, it concluded that the work was not a parody because The Cat NOT in the Hat! did not target the "substance" of the original work.234

Which they won, paying nothing to the plaintiffs and continuing to publish The Wind Done Gone. Which is why I am using it as an example!

I'm no lawyer, but I expect this means that EY is on record acknowledging his creative debt to JKR, and doing so because he thought he was legally obligated to. It seems like it would be hard to argue that MoR is fair use. This shows that the intent of the work was something the author thought was in range of her copyright, and thus not something like parody.

This makes no sense to me.

EDIT: and specifically, acknowledging the debt is more of a good thing; from one discussion:

Whether the infringer copied the original in good faith or for a commercial interest may contribute to the court's understanding of the context of the infringement.72 Any aspect of the infringer's conduct, including whether the infringer acknowledged the copyright owner or whether the infringer sought permission, can be considered.73 Acknowledgment of a source, however, does not excuse infringement when other § 107 factors are present. 74 Additionally when the second work is a parody, the parodist is neither expected to seek nor obtain the copyright holder's permission.75 Understandably, few authors would grant permission to have their character or their work mocked.76

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