Thats not very convincing. Tyrell has been proven to experiment with the replicant lines. Deckard could have been designed physically weaker, or even given extensive psychological programming.
That's not very convincing, either. That's just a whole lot of handwaving things that don't at all mesh with what we see by saying "Well, maybe he made him different for reasons that are not at all explored".
Though yes, despite director comments and included elements like Gaff knowing Deckard's dreams, folks enjoy the truth being left ambiguous. Like did or did not Tony Soprano get whacked?
I mean, Ridley Scott was basically at odds with everyone on that view, so saying "despite director comments" misses that the alternative goes against the actor, writer, and others. I also think it utterly neuters the ending, which is basically par for the course with Scott: A good director, but he has to be kept from ruining the movie by other people. When he doesn't, you get stuff like
Prometheus.
And the Gaff-Unicorn thing was always kind of weak, anyways. The dreams about unicorns aren't anything special, it's Deckard's subconsciously knowing that he's seeking something he can't find (satisfaction, meaning). Meanwhile, throughout the movie Gaff is making those things to mock Deckard: the origami chicken, or the man with the erection. Why start suddenly revealing dreams? He's making a metaphorical commentary on his love of Rachel, or that he managed to find Rachel at all, is an unlikely, almost mythical thing. No replicant needed, it's just a thematic tie-in.
Ridley Scott said he is, that is how Gaff knew to make the unicorn, because his memories are implanted like Rachel's. I own every cut, even director's cut with commentary, I also have the soundtrack, and saw 2049 twice. If people want to say he isn't that is fine, though officially he is.
The writer, actor, and everyone else on that production disagrees. Hell, the unicorn-part wasn't even added back in until a decade later. The whole idea about Deckard as a replicant is largely just Scott being Scott: too clever by half.