Option 1: Give Bustard heavy battleship slots. Two of them, swap the two existing cruiser slots for heavy BS ones, so it can mount battleship cerbs and be poor man's siege platform. The arcs are already bad so I really doubt it could be actually used in pvp.
That way everybody can besiege bases (if he gaters enough players, that's it)
Option 2: New "special" ship available for everyone with some BS cerbs. Remodelled battletransport with a couple of heavy BS slots. Available for everyone like Bustard is.