I don't know if Kenshin propagated it, because I've been hearing it since before he was on the internet - but it may have been him.
I have been goofily trying to catch a non-existent kick from both a flared elbow and tighter elbow and I really don't think there is going to be a meaningful difference between them considering your arm is always going to be faster than your leg (unless something has gone horribly wrong).
I was training with Damien Alamos shortly before he announced he was coming out of retirement, and we spent a lot of time exchanging and catching kicks and his preferred stance to each is the rear arm close to the body and the left arm higher and slightly extended (sort as if you were holding a knife pointing out at about face level - there wasn't any delay in the speed I could catch a kick, even as someone who was adopting a stance I'm not familiar with.
Yeah it's really weird. I also think that people commonly misunderstand the difference between being a boxer, and being a puncher. There aren't many Thai's that have the same fearsome punching you'd expect of a kickboxer, but I usually find that Thais are better BOXERS in that even though their punching form is normally lacking, they do have a better understanding of distance and range and how to set up those punches. Good kickboxers like Cro Cop, Peter Aerts etc understand that whereas a guy like Robin Van Roosmalen would just swing and win because he's powerful.
So I'll see guys in the gym who are doing bag only rounds trying to 'improve their boxing' but what they're actually doing is training their punching power, I usually tell them that they'll be better off in a boxing gym, or working with a coach who understands boxing as a separate sport.
Another I see a lot is the stiff leg muay thai kick, because so many people hear 'we don't bend the knee' and take it literally, rather than what it actually means being 'we don't chamber'.