I agree that JY's explanation for why B is wrong is lack-luster at best lol. But I think you can see that B is wrong by considering what it means for something to not be "relevant". It is not that Haynes being the worst inspector is entirely irrelevant from the concept of how many defective products were inspected by him. If every defective product returned was inspected by Haynes, this would be pretty strong evidence that Haynes is the worst inspector.

Young instead responds by challenging the pressuposition that because >half were inspected by Haynes, Haynes overlooks more defective products (as a proportion of those inspected) relative to the other 2 inspectors. I don't like JY's explanation because he imagines that the three inspectors each inspect 1/3. But this is not technically the presupposition in West's argument. The presupposition is simply that Haynes' products being >half of the defective ones reflects some disproportionality (i.e. he inspects less than half of the products). This is what Young denies in his response.

B seems tempting cause it feels like this makes the conclusion "irrelevant" to the premises–and in a sense it does (as does basically every challenge to an argument). But it does so by denying the pressupositon which makes E a much better answer. For B to be the best answer, it would require a much more immediate dismissal of the conclusion as entirely disconnected from the premises.