You seem to be forgetting the Gemara in Makkos 10a which says that the studying of Torah is what effected the success of the soldiers far away on the battlefield.
Without seeing the whole conversation, I would think this was being used to show that spiritual effort is just as important as physical effort. There are other well known sources that Torah scholars shouldn't be drafted. As for your point about what everybody else in the Midbar was doing and why weren't they all davening/learning, that is a good question.
The drushim come to encourage and emphasize Torah study and prayer and not to establish halachic parameters for the army service.
The rabbies are conserned that the army service and secular education will weaken the Torah observance and study. They don't say so openly, but that is the undelying thinking for their shita and these drashos. Some may actually believe in it, but many don't. But it's not what the droshos are about.
You seem to be forgetting the Gemara in Makkos 10a which says that the studying of Torah is what effected the success of the soldiers far away on the battlefield.
The quote from the Gemara is:
אָמַר רַבִּי יְהוֹשֻׁעַ בֶּן לֵוִי: מַאי דִּכְתִיב: ״עֹמְדוֹת הָיוּ רַגְלֵינוּ בִּשְׁעָרַיִךְ יְרוּשָׁלִָם״? מִי גָּרַם לְרַגְלֵינוּ שֶׁיַּעַמְדוּ בַּמִּלְחָמָה – שַׁעֲרֵי יְרוּשָׁלַםִ, שֶׁהָיוּ עוֹסְקִים בַּתּוֹרָה.
# Every derush has a reasonable explanation
Without seeing the whole conversation, I would think this was being used to show that spiritual effort is just as important as physical effort. There are other well known sources that Torah scholars shouldn't be drafted. As for your point about what everybody else in the Midbar was doing and why weren't they all davening/learning, that is a good question.
The drushim come to encourage and emphasize Torah study and prayer and not to establish halachic parameters for the army service.
The rabbies are conserned that the army service and secular education will weaken the Torah observance and study. They don't say so openly, but that is the undelying thinking for their shita and these drashos. Some may actually believe in it, but many don't. But it's not what the droshos are about.