they just hit like they fell of a 20 ft roof
Pretty much exactly as it is done today. They hit at about the same velocity of a 20 ft free drop.
Military for standard Paratroop drop still uses a round main, only slightly steerable, and without the ability to flair it like a parabolic sport chute.
Some military units, like the HALO jumpers use a newer chute, but for mass troop jumps, its the old canopy. They continue to do this for a few reasons. They do most jumps at night, don't want them flying away from the drop zone, dont want them slamming into each other, want the troop to get down fast to minimize time hanging under canopy and getting shot at. Injuries are unfortunately not uncommon, but I guess overall the minds in charge have thought the risks of round drop fasts are less than the risks in steerable soft landing chutes in a combat situation.
I have heard they the military is looking in the not to distant future to changing towards the new chutes. There would be some advantages as long as the training is done right, and I suspect it will be.
dago