And yes, I refuse to believe you when you state gedolim are against this premise of the Torah. I ask you name one gadol that clearly states we do not need to follow it.
Of course no gedolim argue on derech eretz kodmoh laTorah.
Of course no gedolim argue on the Navi.
Yet, they don’t say the משברך and rarely send talmidim (or anyone who asks) to the army. With or without a written teshuvah, those are clear and obvious facts.
The only logical conclusion is that they hold that derech eretz does not mean to go to the army or say that specific tefilah.
You are in fact arguing on them if you think we should be going to the army or saying that tefilah or that not doing do is a lack of derech eretz.