17's are doing the same thing the Hercs are doing. Dirt strips, most of the airdrop. The J's have most of the same cargo limits the E's-H's do. Floor limits, roller limits etc..
There seems to be some rumor that Hercs are doing all the Tac stuff. It's far from the truth. Yes I know a 3000 ft runway which a C-17 needs is more than what a Herc needs but a C-17 crew did take 87000 lbs into Panama and landed in 1850 ft.
If you look a the cargo carrying capabilities of the A400 it's pretty good. If it works as advertised I think a lot of countries will convert. It cost more initially but should pay off latter.