From back when dinosaurs roamed the earth....
Punters stood 14.5 yards behind the line of scrimmage & at most used two steps. YeOldeDeepSnap averaged .45-.5 seconds on the snap & we only had one blocked per season - always off an untouched corner. If snap-to-thunk is 1.5 seconds or less with no whiff/lookout blocks, no way it gets blocked, especially with the current snapper-friendly rules.
Line drive punts usually come back faster than they go out. In '71 we had a P(itcher)-turned-P(unter), a three stepper, who could hit 'em 70 yards, but his punts never got more than 10 feet off the ground, even in practice. Future CocaCola Intl VP Karl "PeeWee" Barnes used to give us fits in practice during Specialty Period running them back vs us. The coverage team doesn't stand a chance. In '71 we made USCe DB Dickie Harris into an All-American when he blocked a punt off the corner & also ran a line drive punt back for a TD. Coupla weeks later vs Army, same punter drops a ball that hits him square in the hands at his waist - punt blocked.
Yes, punt returns for TDs can indeed be on the punter. Hang time really does mean something - it's why you rarely see many punts returned anymore (even in the NFL) 'cept by our opponents.
I'm sure Shanahan is a good kid, but just like what happened with our PKs who couldn't perform in front of eyeballs at BDS@HGF, if he can't be coached or adjust, maybe he needs to hit the portal. Merry Christmas!