And lets not forget that you don't need to actually sink the any Iowa-class ships, a simple airburst by a rather large missile above it's electronic arrays will Mission-kill her.
One more thing, Iowas do have heavy armor. The thickest part of their hull is over 350 mm thick. A PG-7VR Tandem-HEAT warhead can penetrate that. And if you give me the, "it's not just plain steel" speech, then I'd tell you that a RPG-28 can go through 1,000 meters.
Finally, these aren't itsy bitsy bombs we're talking about here that any Battleship can face. If say, the U.S. Govt recommissions the Iowas, you'd theoritically have Chinese and Russian Anti-Ship Missiles as your big bad threat. The P-700 Granit has a 750 kg (1,600 lb+) semi-armor piercing HE warhead which travels Mach 2.5 and has a range of about 500 km.
Simply put, Armored or not, a Battleship is worthless.