PAA, R’ Moshe wasn’t trying to prove the concept of ???? ????? from that gemara, that’s a given (based on other gemaras), he was showing a direct comparison between talmud Torah and physical protection, and that talmud Torah is more important.
I don’t know what R’ Moshe did or did not know about the spiritual dangers involved in army service at the time, or how effective he thought it would be to bring it up, but we really can’t be medayek anything from what you consider an omission.