See, my philosophy on campaigns is that unless it is a historical campaign, players should have unlimited freedom in designing their fleets. If they want 'Iowa only' fleets, then so be it. The way the campaign should be run IMO, is the players are given a max number of FAP points they can spend at the start of the campaign, a minimum # of fleets they have to build, a max size for each fleet. So long as each player meets those criteria it should be fair game.
If a player is given enough points to build say 15 Iowa's and 10 Patrol level Destroyers, and he takes that option building 5 fleets of 3 Iowa's and 2 Patrol Level craft, that should be fine. Another player can take the option of building 5 Yamato's and filling however many more points he has left up with whatever craft he'd like, building 5 fleets each with a Yamato in command of each one and the rest occupied by a plethora of smaller vessels. The two SHOULD be balanced against eachother.
Of course I understand that isn't necessarily always the case, but then that fault lies in the FAP system breakdown(I am entirely for the FAP system, however I think the breakdown's should be a bit more...linear...), where one war point could equal a multitude of possible breakdowns which aren't necessarily equivalent to eachother.