It's been a long time since I read the book and I only read it once so I don't recall all the details you do, but I guess I always thought that Deckhard being so human (along with Baty) supported the idea that the replicants had become more human than the humans who created them and that humans had lost their humanity.
But, that could just because I've seen the movie so many times and listed to the White Zombie song More Human than Human too many times.