Why US treaty concern centered on ship size

Why were American planners less worried about Britain's large light-cruiser and destroyer fleet than its battleships and larger cruisers?

Their concern centered on ship size rather than the aggregate capability of Britain's smaller combatants.

American concern focused more on British battleships and large cruisers than on the light cruisers and destroyers Britain might sell. That emphasis reflected hull size more than aggregate capability. This narrow interpretation helps explain why treaty debates could understate the value of numerous smaller combatants.