and that’s the one place where there isn’t a physics problem.

Actually there is a physics problem, but it came about after battleships were largely phased out.

The issue is the addition of missiles to naval munitions. They tend to use “plunging fire”, where they try to have a fairly vertical trajectory on impact. That means they’re more likely to hit the deck, not the hull.

Battleships have the bulk of their armor on the hull, not the deck. Trying to armor both the hull and the deck would result in a large amount of displacement (the allowable amount of weight when fully loaded) being used just for armor, limiting storage for ammunition, fuel, crew, and supplies and would severely limit its ability to operate for extended lengths of time.

Sure, a modern battleship could potentially only armor the deck with minimal hull armor, but then that would open them up to guns and torpedos, and missiles could be modified to have more level trajectories on impact.

And to further expand on your comment:

In modern navies, big ships are turning into a liability (The superweapon problem you pointed out). If you have the bulk of your power on a single hull, then losing that one ship cripples your combat effectiveness. Aircraft carriers gain a ton of advantages from being larger to affset those risks, but a battleship is just a big gunship, and that job is better served using multiple smaller cruisers.

And there’s even debates in the US Navy about whether to develop smaller carriers and have 2-3 of them in a task group instead of a single supercarrier. With VTOL and STOL (Short Take Off and Landing) being commonplace with the F-35, Harrier, and V-22, smaller carriers are significantly more feasible than they were 20 years ago.