Well then you are a very smart chap!
This is the intention to demonstrate the greater utility in the CA or the CV, than the BB.
The only thing in your calculation thats of crucial importance is the fact that they fire preemptively every round unless another BB is present. At a 4 its clear that one cruiser will die before shooting and the other 2 will have to stop the bb.
The balance according to our playtest shows with that benefit, the margins are still in favor of cruisers, but its paper thin.
Typically, in AARHE people wont be buying BB’s because of these other choices and this models the historical result. If you think the balance should be equal, then i would look into damage effects, giving the damaged cruisers more serious effects than the BB. I may even make the cruiser 16 IPC.
IN WW2 the BB was overshadowed in its superior firepower but the increased specialization of faster ships with niche capabilities.
I will ask Tekkyy to update the files and actually i will submit the AARHE project to BGG as its own game. But right now we are working on 4.1 rules, then followed by a AA50HE version.