To support what you say, can you show us an example for the MD-80, Litebus. My point is that it doesn't contain diagnostic procedures while it can perfectly list maintenance and operational procedures that are immaterial to the consequences of a misdiagnosis.
If I had access to MD-80 diagnostic flowcharts, I would post the section related o symptom "RAT heater ON while on ground". My reasonable expectation is that it would instruct be to test R2-5 at some point.
I rest my case that proper work an A/C cannot be completed using the MEL only, under both legal and practical aspects.