While I can't exactly disagree with what is being said, and while I freely admit that I never used it for its aa or air building/staging, I think it is a very good unit for:
a) intel (I think this point isn't being stressed enough, the vision it gives is VERY handy)
b) very good torps and the only sub you get (your t2 torps options as uef navy are very good, but are not subs, so very easy to kill)
c) very often forces your enemy to focus its attention on ground-firing it, which gives the rest of your navy more time to hit the enemy fleet (an argument could be made that given your battleship hp, it doesn't matter much, still), and often it's enough to move it a little to make their battleships completely miss the shots (its weird shape makes it sometimes very hard to hit).
I'm perfectly willing to accept that I'm bad and I might agree that a mass cost could definitely make it "better", but I don't find this unit to be useless at all.