Sort of apples and oranges question.
AT: go light, pack weight ~25-30lbs with 3 days of food and 2L water and all your stuff. 20-30 miles per day once you have your hiking legs. Running/trail shoes.
Selection (at least in 1990): pack was 55lbs without food and water and throw in a rubber duck M16 as well. Rolling terrain. Boots.
Would not recommend using AT thruhike as a pre selection training tool unless you have a bunch of weight to lose. Too high a chance of having a repetitive use injury. If did some sections with the current recommended training load, AFTER you are in good shape, would probably be a more reasonable plan.
Infantry/ SF prepares you to be a great lightweight to ultralight hiker because you are already used to spartan field living. With hiking you can really pare down the weight because you dont have to carry 110lbs of mandatory lightweight gear, batteries and bullets.
Claro como fango?
Isaiah 61 KJV