In general, I think this debate is ignoring a lot of factors. Sure, it's probably not a good idea to red shirt a kid who is a 100% lock to leave early for the draft, but when have we ever recruited one of those? Even Blacklock and Reagor weren't 5* sure fire 1st rounders as incoming freshmen and they may be the two best players we've ever had. Since you can't know that critiquing a decision to red shirt is Monday morning quarterbacking.
When Blacklock red shirted the 4 game rule didn't exist, which I think would have totally changed the decision on him. We all know now that he was already better than any DT on the roster his freshman year, but it's also not like him playing that year would have gotten us a conference title or playoff berth.
All that said, I think there's little doubt a kid is going to be better in his 5th year than he will in his 1st. Given that, and given you can't assume a kid is going to leave early for the draft when he's only a freshman, you want to preserve red shirts as often as possible.
Exceptions to this general rule are when it's obvious these freshmen are already better than your more experienced starters in years where you think they can help you win a lot more games or you have serious depth issues like we did last year due to all the injuries.