That actually sounds really good! Keep going with the ideas! I'd like to see something like that too.
I see one problem on first place though: For the big and the small ships you need an experienced crew if you think of it like Squid and Galleon. The Pyramidion is an easy ship, so everybody can fly as well as be gunner and engineer on that one, but a Squid and a Galleon... I don't quite think you'd get the teams filled. There'd probably be many games with the Destroyer ships filled but empty small and big ships. Furthermore, if for example I wanna play with some friends but we both like to fly Squids...well, it'd either not be allowed to do so or make balance too difficult to calculate.
Thanks! Glad you liked the idea! One of the devs once mentioned to me that the squid was actually originally a 3-person ship. In any case, it has not been my experience that players shy away from crewing squids or galleons. Especially galleons. A lot of new players jump into the game wanting to have the biggest ship in the sky. I do however think that you might be right about the squids. They have a high skill ceiling, which many players might find intimidating.
Since I don't think that the bosses in the Adventure mode will be playable by humans, I really would like to see them in skirmish at least, so we can use them (or at least one).
Going into the balance issues (and yes, I know you just wanted to present your idea, which is really good!, but just showing every side of the possibility Im gonna write that down too), I don't think that 3 people on a Squid are enough to keep it alive - 5 people on a Galleon though makes it almost invincible as the ships stand now. Only making 1 big and 1 small ship available for every team destroys some different tactis though, and making them available in any mass is...well, just as we do now but with different crews (see above).
The thing with letting the players choose any mass for their ships is that the total crew has to be 12.
And yeah, balancing it would be way hard, but there's a few ideas that I thought might work. What if the larger ships' hull armor was spread throughout multiple components, which corresponded to different areas. This forces more people into the engineering role to keep the ship alive without making it too fragile. It also makes it vulnerable to focus fire. Throw in another reduction in their manueverability, and the result is a ship that is merely specialized, instead of overpowered.
Likewise, by consolidating the vital components of the squid and other frigates, you make it so that keeping them in full repair is much easier, which frees up more time for the engineer to gun. And the reduction in manueverability that the Cruisers suffer makes it absolutely viable for a frigate to sit in their blind spot and knock out their engines.