[unionemployee]

Cargo planes like the C-17 can make a steep “tactical approach” by creating lots of drag, with spoilers, reverse thrust, etc. It’s difficult to get very aerodynamic aircraft to ‘go down and slow down’. That’s not to say that the flying wing design couldn’t have drag devices, but it’d take more to reach similar performance.

The approach isn’t “slow” in terms of aircraft speed but rather its duration. Shallower equals more time in reach of adversary weapons.

[walrus01]

On the other hand, a tanker aircraft typically flies from a much more prepared base, something with a longer, guaranteed to be well paved runway, in non-contested airspace, with minimal or no risk of MANPADS in the area.

The design requirements for a C-17 to operate from a rough field, such as that which was built at camp bastion in Helmand province, are considerably different than for an aerial refueling tanker.

The rough field tactical tanker role is as far as I know presently served by a variant of c130 modified for special forces missions.