Not disagreeing with any of your thoughts because they're all valid in one context or another.
But....
If Merlin HAD used technology in aid of Charis - through the Limpet Mines on SOME vessels route, or perhaps by spiking the artillery that was firing with extra powder to make them randomly burst, or through some of the thousands of little ways that Owl's remotes could have caused "plausible bad luck" or "accidental mayhem" then think of the possible reduction in overall loss of life.
Maybe Merlin didn't want to expose a LOT of Owl's technology, but the odds against Charis were (at least at the OAR stage) pretty significant! He did SOME things to mitigate against SOME disasters (medical nannites, anti-ballistic undies, and battle steel armor come to mind) but other than providing intelligence - at a time when the only things Charisians really knew was that "Merlin sees things" he didn't do anything OFFENSIVE.
It may not be this way for everyone, and I can understand your sentiments, but I personally think it's out of character for a trained tactical officer who lived his/her entire life (up to the point where the PICA recording was first uploaded into the Merlin chassis) in a survival-imperative was that (s)he KNEW was going to be lost - the Gbaba war.