I admit I don't see much use in marines, helicopters, or paratroopers. Helicopters might be useful if the AI built more tanks, but they don't seem to. Paratroopers and marines just don't have a valid place in my battle plans.
Cata/treb/cannon/Artillery is really mainly for taking cities now. It can provide supplemental firepower at best in other cases.
I don't see Battleships as powerless at all. They need a destroyer screen to keep the subs off, but they are a staple of late game naval warfare and deadly against coastal cities.
They are obsoleted along with destroyers by missile cruisers, but that is very late game and they never cease being useful. My final ranged navy before victory or defeat is usually still primarily battleships sprinkled with a few missile cruisers.