Talking past each other a bit here. Let me try again.

EY makes it abundantly clear that two agents can have a fundamental disagreement on values

EY allows for disagreement in attitude: you might want one thing, while the babyeaters want something different. Of course I'm not charging him with being unable to accommodate this. The objection is instead that he's unable to accommodate disagreement in moral judgment (at the fundamental level). Normativity as mere semantics, and all that.

Your second point rests on a false dichotomy. I'm not making an empirical claim, but nor am I merely defining the word "reasonable". Rather, I'm making a substantive normative (non-empirical) hypothesis about which things are reasonable. If you can't make sense of the idea of a substantive non-empirical issue, you may have fallen victim to scientism.