I've only interviewed with one company that did a homework assignment "right" - it was time constrained, it was after an initial phonescreen, I was still more on the junior side, and the onsite interview included a follow up on the homework assignment to extend it in some way.

But generally, I agree. There are enough other ways to screen people for basic competency (20 min tech conversation, looking at StackOverflow profiles, etc.) that it seems unnecessary for anyone except junior developers.