I like Chiang's work enormously, and I do think he's an important and underread writer, but . . . no.

I wonder whether that claim may be coming from folks somehow interpreting "living SF writer" as "currently working SF writer." LeGuin's best work, in my opinion, was written in the sixties and seventies, while Delany doesn't write SF anymore. Gene Wolfe I don't know about. But if the question was understood as "who's the best SF writer right now?" naming Chiang is much less ridiculous. Especially if SF is being defined narrowly as pure science fiction.