forget, you write:
And I defy any line engineer, no matter how smart, to raise his hand and say “Hold on guys, RAT Heat on, I bet R2-5s failed and we can’t just pull the RAT breaker because the TOWS might also be inop”.
I have no experience in airplane maintenance, but I believe many good engineers would think exactly along these lines. Just like pilots develop a "pants seat" feeling over time, engineers do the same, actually their most important quality is not only to be able to repair, but to properly diagnose first.
Beside, in this case, there has been a major lack of proper analysis and logic thinking.
A failure in which and electrical device, be an heater, bulb or whatever else, remains ON all the time, it's obviously a failure of the circuit that energizes it, not a failure of the device itself.
The breaker there is really meant just to cut power in case a short circuit overdrawing current, or when there something else wrong with the heater itself.
I know many automotive mechanics that are really unable to deal with even the simplest electrical problem, while others are surprisingly good. I suppose the same happens with airplane engineers, not everyone has the same skills and is equally proficient in all areas. E.g. a local hydraulics guru said to "better not touch electrics", if you get what I mean.
I feel very bad for the engineer(s) that service the A/C that day, but it cannot be contended that they failed to properly diagnose a fault that was very well in their own domain.
Then we can discuss if we want engineers to be smart or not, if was poor design, if we need better diagnostic flowcharts, etc, but saying that the mechanics properly worked on the A/C in case, it's like saying the pilots properly executed the T/O checklist.