First off, if you're going to attempt to make an intelligent post, at least get the terminology correct. There are no "generics" in the biologic space. They're biosimilars, and the first SC biosimilar won't hit the derm space until probably 2021 as Humira's exclusivity patent expires.
Secondly, the only thing Enbrel/Humira have in common with Dupilumab is that they're self-injected SC biologics that derms can prescribe...aside from that, they're used in completely different disease states.
That being said, If the market can sustain a $20k/yr small molecule pill in a disease category with 7 other competitors that are all north of $30k, it can sustain a $30k product in a disease category with no alternative.