“Tarnished” may have been the wrong word. But ISTM that over the past decade or so—certainly since Le Guin’s Cheek by Jowl was published in 2009—there has definitely been a more widespread awareness that the apparent “naturalism” of Watership Down, and its repeated appeals to Lockley’s nonfiction study of rabbits to sound more authoritative, are misleading.
It’s part of a general increased recognition of longstanding sexist bias in the study of animal behavior, where human gender stereotypes color researchers’ impressions and reports of what nonhuman animals are actually doing. Adams wasn’t just telling a particular adventure story that focused on male characters and an imaginary non-naturalistic masculinized-militarized setting (the “Nazi rabbits” of Efrafra warren): he was misrepresenting the whole nature of sex roles even in what he described as “normal” and “natural” forms of rabbit behavior. Female readers may tend to notice this more strongly than male ones, natch.
Oh definitely, I’m not arguing that it should. I’m just saying that recognition of its fundamentally sexist assumptions is a bigger part of popular awareness about the book than it used to be, AFAICT.