There are a lot of unsuspected things going on around the area of the join between the neck and body. Some makers regard the thicker parts of a guitar neck as being “unbendable”, but the bending forces in the neck near the body joint are higher than at any other part of the neck. The neck and heel are usually made of quite a "soft" wood, and will distort quite easily, even if it is much thicker at that point, so bending certainly does take place, and even a tiny movement at that point has a considerable effect on string height. Not many makers take this into account.

Most truss rods do not influence the angle of the neck to the body because they usually have nothing to anchor to beyond the neck joint, and slowly but surely, the angle between neck and heel will open out under string tension. This is one of the two main factors in “neck rotation” that might justify resetting the neck to a new angle after a period of time.

Something else that is not often noticed is that higher actions put a much higher stress on the upper parts of the neck. This is doubly unfortunate, as it means that once distortion starts, the stresses can become even greater.

Looking at an old Gibson mandolin will show the extra material that was left in the area where the neck blends into the heel shape, rather than the deep sharp “throat” of many newer designs. It’s a theory of mine that old instruments are well regarded partly because time has filtered out the bad ones into the rubbish bin, and Lloyd Loar mandolins have survived extraordinarily well. That extra wood looks lovely but serves mainly to reduce the stress in the neck at the point where the bending forces are greatest.