If you look back through Onishi's oeuvre you'll find that he has no great interest in Buddhism (he did write a piece back in 1996 on a Temple in Brooklyn). He does, however, have an interest in vaguely leftish, "modernizing" pro-western critiques of what he sees as silliness and backwardness in Japanese culture. He is basically selling a 21st century variety of journalistic orientalism.
There might be some truth to some of the things that Onishi has to say - but the fact is that he seems to *want* Buddhism to die out, and is simply trying to hurry the process along a little by peddling a very depressing assessment of the current situation.