Unlike the Reddit thread which wanted a week’s worth of work, giving ~4 hours is reasonable, especially since that’s close to the overall opportunity cost of a normal in-person interview.
First off, the company's representative here is wildly unprofessional. You cannot be that hostile when representing your organization, even in the face of such a hostile post.
That said I actually don't necessarily disagree with his initial point. Exploitative would be if they were having candidates do work that would be used by the company. I don't think there is anything wrong with asking people to do a demanding challenge as part of an interview, provided you are willing to accept the candidate loss you will get from people who refuse to do it.
I checked the assignments and they looked reasonable to me. I've done a far more complicated assignment for my current contract, and to be honest, I prefer these type of assignments to "whiteboard" interviews.
