Muscle testing (Kendall’s method) is likely the best approach for upper body testing. When testing the upper body I’m not that interested in precise measures and ratios (although I use them with advanced athletes) but rather by obvious red flags like poor activation of a key scapular muscle or a significant left to right imbalance.
Structural balance is an interesting tool but it has its limitations; results can be influenced by training habits and levers and can be very long to do. Furthermore going up to a 1 or 3RM during an assessment cannot be done with everybody.
For upper body I normally use muscle testing for trap 3, trap 2, rhomboids, lats and external rotators and body proportions (wingspan vs. height, ulna vs humerus). These have more direct implications in exercises selection and are easy and quick to do.