I am NOT promoting realism for the sake of realism in this game. Yes, it is not a sim, and never will be. This is a sandbox game about having fun. Absolutely correct.
And "battleships" turning like fighters is not fun. It is immersion-breaking.
Main thing is: in this game, ship's stats do depend on design of your ship. You are trying to pick one stat (maneuverability) and say that is should be possible to have any desired maneuverability, no matter what ship you build.
"Sandbox" don't yet mean "i should be able to build anything and then assign to it any desired stats no matter what".
If we continue your idea, next logical thing to say would be:
"hey, i want to have a miniature ship, 10 meters long, and i want it to have 10 million shields! Why that is not possible? This is the game about having fun or what? That limits my creativity, i want to be able to create small but indestructible ship!"
That would be exactly as valid as your statements.
The thing is they can have massive manoeuvrability but it look damn ugly what they seem to want is super creative blocks with super stats, ask the dev if he'll add creative blocks for single player :P