agreed. Although, at times, one has to Lock -IN on one area or two at a time, due to Extreme tightness or such. Once that muscle is under control, next thing another one can be looked at or even only Found once one Above it has settled down.
eg
Some guys Traps are that Tight Overall that you cannot get in deep enough to find out if their Rhomboids are ok or not. Might take sometimes a whole session just to relax the Traps! (as an example)
Your right though, esp once healthy, everything must be trained as a unit. eg, After doing an upper body workout, its good to finnish off with some inn’ies and out’ies rotor cuff work. And same with the hips. It only takes a few minutes extra