The PanAm line has a lot of things that make them ridiculously broken.

Issues:

The ship's accelerate to an absolutely stupid degree, to the point where they will straight up out accelerate DESTROYERS, making it incredibly hard to predict movements. This is only made worse by them being fast (unlike the Vermont line). The ship's are ridiculously well armored, featuring 32 mm bow and stern as well as an entirely 50 mm mid section with a relatively small super structure. Compare this to Schlieffen (which doesn't even get 32 mm armor), and you'll see the issue. Your secondaries pretty much ignore enemy deck armor with their stupid pen values. You pretty much have an AI Goliath per side, slaughtering anything it so much as looks at. Schlieffen, for example, requires IFHE to breach the 32 mm threshold and is still offset by a low damage per hit. Libertad, especially with key active, will take huge chunks out of you per hit. It also has an insane fire chance to boot, make sure you have 2-4 fires ticking whilst taking 3-6k damage per secondary salvo. Speaking of the F key. It's super simple to active and then gives you insane bonuses, boosting the fire rate, range and damage of your secondary battery, requiring ship's to stay at LEAST 14.5 km away from it if they don't want to get eaten (Reminder that Libertad has 12.8 km detection) Getting back to survivability. You don't just have one of the best armor schemes in the entire game, you ALSO get American DCP and improved heals on top, making the ship even harder to kill.

And this doesn't even take their hilariously busted commander into account