Tiger cruiser armament and a distinct secondary battery

Why was a Tiger-class cruiser proposal combining 6-inch Mark 24 guns and 4.5-inch guns rejected?

The guns were wanted for other uses, and the cruiser needed 6-inch armament with a clearly distinct secondary battery.

The rejected proposal combined a pair of 6-inch Mark 24 guns with six or eight 4.5-inch guns. The explanation given is that the smaller guns had other demands on their supply, while the cruiser required 6-inch guns and a clearly distinct secondary battery. That distinction concerns the guns' roles and ammunition. A later clarification contrasts this preference with a tentative recollection that an Atlanta carried two different types of 5-inch gun. The Atlanta detail is explicitly recalled from memory.