In the military all we had were fixed 10Xs with mil-dots or mil-rads or similar variation to the theme.
You are instructed to take shoots from 100-1000 yards hence a fixed 10X with mil-dots does the trick. Adjustable power is a no-no in combat because the mil-dots calculations vary with different magnification plus it's much better to learn to shoot accurately using a fixed scope and use the mil dots to adjust for bullet drop. It was never a case of durability as I believe quality variable power scopes can be just as sturdy as fixed one.
The objective of a sniper is to kill zombies with one shot any any distance not to nail groups of 1" at 1000 yards. Past 500 yards we were instructed to take body shots not head shots. Said that, I've seen 1-3" groupings using 10X @ 1000 yards! However, if you ONLY shoot at 1000 yards, then you'd be better served by higher magnification like a 16X or 20X.
A 16X would do the trick from 500-1000, a 20X 700-1000, but a fixed 10X is where it's at in terms of sheer adaptability and that's the whole point of being a soldier: Adapt and Survive!
So yes, for 99% of shooting and hunting situations, a fixed 10X is all you'll ever need.