Why larger heavy cruisers would affect US and Japanese light cruisers differently

Would 10-inch-gun heavy cruisers make US light cruisers grow while Japanese light cruisers stayed broadly unchanged?

Possibly: US combat requirements and industrial capacity favor growth, while Japanese numerical needs and limited infrastructure constrain it.

Heavy-cruiser growth does not mean every light cruiser must also become larger. The US Navy might favor bigger light cruisers because it treats them as aggressively armed combatants and can expand the infrastructure needed to build them. Japan needs numbers as well as individual capability and has less spare industrial capacity after funding its other warship programs. The two navies could therefore respond differently to the same heavy-cruiser benchmark.