Gun calibre was only part of the difference between the designs. Lion carried almost two inches more protection across the armor categories compared here. That margin reflected a different combat expectation: Lion was intended to stay in a fight with enemy battlecruisers, while the Indefatigable type was not. The second-class assessment concerns their relative ability to fight peers, despite Australia and New Zealand remaining capable ships.
Notable Point · 8:38-9:09
The armor gap behind the first-class label
The Lion type's roughly two-inch advantage across major armor categories helps explain why it could stay in a peer battle that an Indefatigable was not designed to fight.