Why carriers make poor battleship conversions

What would Essex- and Illustrious-class carriers look like if converted into battleships?

They would make poor battleships because carrier hulls retain battlecruiser-like proportions and stability arrangements optimized for high flight decks rather than armored gunships.

Removing the flight deck would not undo the structural and metacentric-height choices made for aviation. A workable conversion would require such heavy modification that the apparent shortcut largely disappears.