How is it a viable idea to base the balance on credit cost? Battleships cost a lot, -because- they take multiple players to take out and need to be restricted (otherwise the majority of the server would pilot them). While people may complain about bombers being overpowered, they can be killed by a single fighter. A battleship requires at minimum two bombers to beat it, and likely three to have much of a chance against it. That is three players just to defeat one, simply because he purchased a more expensive ship. In your proposal, it is not fair for players to be forced to muster 5 + specialised ships just to have a chance to against someone who flies something worth nearly a billion credits.
Capital ships are not obsolete. People need to take time to train their skills, test the weapons, and submit their valid concerns to the development team. Whining about the effectiveness of weapons does not help - test them out more in all different situations and form an opinion based on evidence, not how you got ganked by bomber pilots.