Correct me if I'm wrong.
It is not a matter of download on the horizontal tail, but of the difference in angle of attack of wing and horizontal tail.
A straight-wing aircraft needs a horizontal tail with a negative angle of attack (lreading edge down) relative to the wing for dynamic longitudinal stability (leaving canards ou of the discussion).
Under normal circumstances that will indeed result in a download on the tail as well, although the C172 example shows it's not a given.
The story changes with swept wings, and a fortiori deltas. For various reasons these are (or can be made) dynamically stable in pitch, so there is not need for a tailplane for stability.
The average 'modern' airliner has a tail for improved control, trim, etc., less so for stability.
So I would expect under optimum cruise condition to see only small up- or downloads on the tailplane, and considerably less than on an equivalent straight-wing aircraft.
A trim tank can be used to move the CoG and hence minimize trim drag.
CJ