His ship is best used in combination with other empire ships. TIE bomber is a key part of any empire fleet, and the others help to support. IMO the best part of his kit is the undispellable target lock. That effectively leaves the TIE bomber on perma-taunt, and spreading around the TL also means through bombers unique that you ignore more and more of your enemies defence. Vader's unique means that any time you attack a locked enemy you gain 15%TM, keeping you taking turns. The synergy with other TL abilities for TIE, TIE Int, the Palpmobile and more is why his ship is useful. On its own and without synergy to other empire ships, that's when it falls down a bit.