If authorial intent means anything, as well, in the novel Dick explicitly says Deckard isn't a replicant. Granted, this is an adaptation, but it's close enough to the novel in theme that I think the point stands.

Completely agree with your points sellew. My usual argument is that Deckard is too human (in terms of physical abilities) to be a replicant hunting other replicants, he's weak compared to even a 'pleasure model' for instance, but your thematic argument is much better.