It's been pretty clearly demonstrated at BoM that RMN ships are not sufficiently survivable against mass MDM fire. If all of home fleet had consisted of the same mass of BC(P)s they would have done quite a bit more damage to Haven and died pretty much just as fast. So the RMN option is either to plan on their SDs having a combat lifetime of under 15 minutes or finding a better solution to the defensive issue.
They have chosen B, but exactly what this consists of has not been shown. And given the path of the books, I have no idea when they will possibly run into a situation where they will need to demonstrate this capability.
Right, because being massively outnumbered in podlayers is clearly a fair fight from which solid conclusions can be made...