How larger capital ships could raise the cruiser calibre ceiling

How might cruiser designs change if this alternate timeline produced much larger-gunned capital ships?

Cruisers might plausibly move to 9.2-inch guns, while 12-inch battleships would lose credibility if a cruiser could approach their firepower.

The answer projects the consequences of a more heavily armed Queen Elizabeth class and an 18-inch Argincourt. Hawkins might have moved beyond 7.5-inch guns, with 9.2 inches a more plausible practical ceiling than an attempted 10-inch cruiser gun. Treaty categories and ship roles depend on relative fighting power because a capital ship only slightly more heavily armed than a cruiser loses much of its rationale. Changing the capital-ship benchmark could therefore alter cruiser design and the definitions used in naval-limitation agreements.