Is this the same as saying shoulder tilt determines barrel path? (or maybe just from launch through extension)
re: BR philosophy - I've been catching up on some BR podcasts that past few days - and recently they've been emphasizing the use of the RR to help teach an athlete how to move (with the focus on the turn), more than "use this device, then do the same thing with a bat in your hand". As I understand it, their methodology is to teach the movement (progressions) first, and not move on to the actual swing until the student can correctly replicate the desired movement.
I would also say that I don't think they've changed their thinking much over the years. They were one of the first sites I discovered that discussed launch angles, and an upward swing path. Don't really see how that's changed (at least since ~2014). If anything, they've become more open with their methodology, which apparently they were very protective of until recently.
Lastly - re: hands leading the core - this may be the same thing FFS was referring to regarding first and second engines - but hands first seems to be putting the cart before the horse(power). Wouldn't the core just be playing catch-up for the rest of the swing? Doesn't that reverse the power source in the kinetic chain?
BR swing was momentum based in their earlier instructions. BR couldn't get their hitters onto their front side/foot fast enough. They've since changed that but, that was my biggest 'beef' with them at the time.