Why the Admiral class carried such heavy armament

Why were the Admiral-class battlecruisers designed with such a heavy gun and torpedo broadside?

They were intended to hunt the enemy battlecruisers attacking trade, making them anti-battlecruiser ships as much as commerce-protection vessels.

The unusually heavy gun and torpedo outfit makes more sense when the ship's protective mission is included. Enemy battlecruisers threatened trade, so Britain needed a fast ship able to find and defeat those raiders. The concept resembles Tiger and is described as an anti-battlecruiser battlecruiser. The label clarifies why commerce protection could demand a ship that looked excessive if judged only as a line-of-battle unit.