Smollett, while I agree with your math, I would say that mid-range (1.5km) build with a merc is a dangerous build. 1.5km is very easy to close (2v2 Dunes before latest spawn release), and without the gat, your close-range effectiveness is greatly diminished.
I would say that build relies upon lots of open air behind you for back peddling or a teammate who is capable of surviving 2v1. I would also say against an opponent who is indecisive with their engagement strategy it can quite immediately lay waste to their ships. Against a more cohesive and thought out offense, however, it loses potency. I personally only bring it on a Galleon for this reason--I have another heavy emplacement to bridge that close combat gap.