The problem isn't "waaaaa he sunk my ship!', its a game and one of the features is to destroy and sink ships. No, the problem is HOW the ship was sunk. Yes it is the defending teams responsibility to defend the ship. There is not enough people around to gun....oh well !! I guess if the attacker is any good, the ships going down.
The problem is the dive bombing heavies! Its a gamey "short cut" for those who are to lazy to learn/practice to do it the conventional way (level and in the bomb site), or are caught up in the bomb/bail/repeat "gamey" mode. Divebombing is an easy sure way to take out the CV. There is no penalty for dieing, so it takes all chance away from the equation. If a heavy is forced, due to coding to come in level for his run there is a "possibility" he will miss. Figuring his angle of approach, the possible movement of the CVs evasive maneuvers, and such would even the playfield a bit. It would make up for the CV group not having a standard cap, or hundreds of guys standing by to man the guns.
Its just another easy gamey play, much like the "stick the gun of a GV through the fence" trick, or the "turning down the graphics" trick, or the "control the buff guns from F3 mode" trick, or the "go for the HO with your cannon ride because you don't know what a BFM is" trick.