Why the US and Japan wanted large carriers

Would small first-generation carriers keep the US and Japanese navies building small?

No; both navies already valued large air groups and rapid mass launches, and their strategic planning pushed them toward bigger carriers.

US war games treated Langley as too small and favored the large strike wing, while Japanese analysis reached similar conclusions about concentrated air power. Japanese plans for a Mahanian decisive battle against the United States differed from plans to counter a British blockade associated with Corbett. Carrier design grew from the expected campaign rather than simply copying a foreign hull.