As for the full power from glide descent, well, of course it's done smoothly, not rammed
Though the 172 does not have defined "Abnormal Procedures" that it what doing this would be. Under most atmospheric conditions this can be done with no harm in a 172, but that does not make it goo practice in a 172, or any other piston powered aircraft. If you do this in a turbo 210, the owner is going to rap your knuckles!
If a pilot has mismanaged their descent so much that glide descents are required, that's simply poor planning. Back in my turbo Aztec days, the requirement for descent power was to decrease by 1 inch of manifold pressure (which would roughly equate to 100 RPM - fixed pitch) per minute. A faster power change was considered potentially harmful to the cylinders, and an abnormal procedure.
Though turbine powered aircraft, which would include the military pilot's PC7 are capable of rapid power changes without harm, that does make it "good", smooth, or appropriate technique. Military aircraft and training are aimed at a very different role for the aircraft, and "smooth" and caring to the aircraft may not be elements of that training or technique.
IF, a power off glide is necessary because of botched planning, or some type of quasi emergency, then yes, flying the resulting glide at a slower airspeed is better for the engine, that rocketing down at idle power and cruise airspeed. Damage from shock cooling is very real, occurs in seconds, and is very expensive to repair. I once had to rapidly descent a Cessna turbo 207 because I had spotted a boat in distress on the lake. Though I closed the cowl flaps, and was still "gentle" with the power reduction to idle, and slowed the descent speed (reduces undesired cooling) I was stunned at the incredible rate of cylinder cooling indicated by the cylinder head temp indicator. I immediately though back to the 1 inch of MP per minute, and was reminded of the wisdom of that.
All that being said, as I read a lot of the foregoing, I see lots and lots of numbers, but little sense that the pilots are simply flying the plane. Is this a result of pilots spending hours in front of computer flight simulators before or in the midst of training? I opine that there is a shift in the emphasis away from to plane itself, and toward all of the information that today's indicators provide. Take yourself back to the Tiger Moth, the airspeed is indicated out on the wingstrut, and really is not that accurate anyway, and the tachometer really does not work that well either. I very much doubt that Tiger Moth instruction and operation was filled with all of these numbers!
Just feel the plane, listen to the engine and the airstream, and watch where you are going. During VFR, this should be all you need to fly very well! During my Caravan type training, I had a training pilot who was fixated on numbers. I got frustrated enough with this that I covered the airspeed indicator, and flew a very presentable (and totally safe) circuit. If you
need to look at the airspeed this often, you need to improve your skills.