Yes, he is a niche writer. He deals primarily in fantasy and magical realism. He was best known, for the longest time, for his graphic novels.
I'm wondering which Watership down stuff you saw, i.e. the original film or the horrible series thing they made? The film is not the least bit family entertainment.
It is outright horror. How it got its original rating defies logic. Now there was a watered down, simplified art series. I can't help but think that is what you are talking about. If so, I advise you to watch the original film release.
That and they are just lazy. They have the rights to keep using that title and to do otherwise would require them to use an ounce of creativity to come up with their own. That is an ounce more than they actually have.