Torch could work with even RMN or RHN light ships that would otherwise be retired because they could not be retrofitted with the MDM. That should be sufficient to handle much of what could be expected to try and make a pass at Torch for other than a second revenge hit by the Alignment.
Recall that most of the rest of the known galaxy is working with variations of the SLN weapons systems and ships. How much of a target -for anyone but the Alignment- is Torch? Against your garden variety pirate (not the big multi-ship fleet operations) a couple of DDs and or CLs combined with modern LACs make for an expensive place to hit. They also have Erwhonl and the Maya Autonomous Area which could have warships trading in and out doing "commerce protection" so somebody trying to invade Torch and take the systems would be playing a high stakes game.
Perhaps the Royal Torch Navy needs a couple of ships (armed) that can carry enough people to crew captured slavers etc and use the captured ships both to bring the liberated slaves back to Torch and then either convert the prizes for merchant shipping or sell them for funding other needs. At the moment they can -a frigate is armed so an unarmed freighter is not that big a problem unless they are willing to blow themselves up rather than surrender-so a frigate of two with a support ship hanging outside the hyper limit could be carrying prize crew. What they will need is enough experienced people to crew those ships going out in the first place.