Why a light cruiser could threaten Lexington

Would a light cruiser be a real threat to a Lexington-class battlecruiser because its smaller guns fired more quickly?

Yes, but the principal danger would be its torpedoes rather than the volume of fire from its guns.

A light cruiser did not need to defeat Lexington in a conventional gun duel to pose a serious danger. Torpedoes could outweigh the battlecruiser's advantage in gun caliber. The comparison shifts attention from rate of fire to the weapon capable of producing the decisive hit. Warship matchups cannot be judged by gun counts alone.