Just to make a quick backtrack:
A free for all sounds like something that could be quite fun with 8 ships in total.
Personally, I don't think so.
A free-for-all completely negates the need for harassment ships, disablers, or any other support loadout; one player would do all the work on a kill, and someone else would swoop in and take the point.
Free-for-alls would be made of Merc/flack Pyramidions, gat/flack junkers, and, maybe every once in a blue moon, a gat/mortar Pyra.
While crew-based teamwork would be maintained, team balancing of ships and captain coordination (two major parts of the game) would be out the window.
Making a shaky alliance between another ship to take down a Galleon would be interesting, but coordinating the strike without alerting your prey to your plans would be hard to implement.