Rivendell expresses a lot of strong opinions on a lot of things, some of which make fairly good sense to me, some of which don't. As for the claim in this article that nearly everyone says you can power through 360 degrees of a pedal stroke with the use of clipless pedals, I've never actually heard that myself. They go on to say that all you stand to gain with clipless is putting less downward force on the pedal, which means you're fighting the other leg less. But then they say you actually can pull up on the pedal while using clipless during very steep climbs, and that this is indeed an advantage. Well, considering that very steep climbs, to me, are where you want all the advantage you can get, I'd say that's significant in itself.
All in all, I'd say the article is really just one person's opinion, written in a way that pretty much ridicules anyone who prefers clipless pedals. This, of course, plays right to the notion that retro-grouchy is almost always best, a Rivendell mainstay. I think this particular article is mostly BS-