I regularily sink CVs with pt boats 40mm, and I must confess I enjoy doing it.
But I do agree with this: Ships should only be damaged (with the exception of guns) by torps or bombs.
In RL you could strafe a CV all day and all night with airplanes, and just make it into swiss cheeze, but never would you sink a cv by strafing alone.
bombs and torps should only add to the ships "damage" total.