Yeah, so, I understand protecting the integrity of the body is the main priority in running a waterfall. I'm a big fan of the "Oregon tuck", and practice it every chance I get. But on a few occasions, I've ended up executing the lay back technique and had some of the softest entries- like a diver.
Boofing is great, especially if you have downstream hazards to navigate. But you can also take a hit with a boof. And from altitude, I've seen people crack boats from the sheer thump of the boof.
Vis-a-vis broken backs, it looks like people break their backs more when they go for a tuck, but don't quite launch right and their bow starts to drift up. The instinctive reaction seems to be trying to "stomp" the bow back down, which leaves the paddler with a vertical spine on impact and a boat angle that is closer to a boof than a pencil.