Limiting them to 1 per account would not stop people either as long as they use the FAM. The most reasonable way to make them used more rarely and for more purpose based is to tweak their stats, their weapon stats and purchase cost accordingly. I havent added anything new here in fact, ppl have already stated similar beliefs. Yet, in my opinion a battleship needs to mean a strong but slow and unagile target. Actually I cant accept the idea of having agile battleships with the same energy output of 7 million. Just increase their hull a bit and make them slower and more stationary so that they would need to have or hire escort ships or wingmen whatever you call it nearby.
On the uncharted lagoons of anguish, I sail with a canoe made of my sins.