In some 300+ G40 games, I’ve never bought a battleship unless the game was already won I could do whatever I wanted.
2ftrs, 1 cv= cost 36, 6 attack, 10 defense, 4 hit points.
2 Battleships = cost 40, 8 attack, 8 defense, 4 hit points.
Pretty clear, building a fleet around battleships maybe slightly be better on attack, but otherwise are blown away on defense. And defense is mostly what matters with fleets, since if you are attacking you usually can and should use land based air to bolster your attack.
Plus if you are going all attack with ships, subs are the way to go: 36Ipcs = 6 subs, 12 attack, 6 hit points.
I rarely buy cruisers, but I sometimes buy tac bombers if I’ve got a leftover 1 IPC at the end of purchase and convert a fight in the cue.
I agree, tacbs should be 10. They aren’t really any better than Ftrs, or maybe even worse since their 4 attack is only achieved through matching.