In Vanilla we also had Junkers flying in the best case a CSV, nowadays they have a shipline that spans over nearly all snub classes, a unique cross-breed of Transport and Gunboat and their very own Gunboat.
Corsairs and Outcasts that had only fighters and freighters, and nowadays have whole battleships. You dig my point, yes?
So no, it's not completely out of the line for GMG to have a Gunboat, in fact it even makes sense.
You know how hard we had to fight for that boat? Especially since we had no in-lore reason not to have one like the GMG? Junkers have done huge amounts of work to make themselves the most dominant faction on the server, so they deserve a few perks.