I'm going to argue the other way. The threads are in shear when the
"bolt" is in tension, as well. Just that the shear is going in the
other direction.

Why should thread shear strength matter? You just increase the number of
engaged threads to get the strength you need, for any thread type.

As regards buckling strength, you're correct that UNC beats Acme for a
given nominal size, but only slightly.

Stress area of a 1-1/4 Acme screw is 0.907 in^2.

Stress area of a 1-1/4-7 UNC bolt is 0.969 in^2.

(_Machinery's Handbook_, 26th.)