Not researched and working from hazy recollection, but I seem to remember that torpedoes and torpedo employment may have been significant factors in the outcome of this battle. Torpedoes and close-in night combat were big parts of Japanese Navy surface tactics well before radar became available, going back to the Russo-Japanese War, and pretty much every Japanese surface combat ship - heavy cruisers, even battleships - had torpedo tubes. They also had excellent and lethal torpedoes.
OTOH the US Navy had for some reason (maybe more open-ocean history and less archipelagic?) decided prior to WWII that any surface action between cruiser-and-above combatants was most likely to be a long-range (gun) battle where torpedoes wouldn't be important, and to save weight took the torpedo tubes off everything but destroyers (not sure about light cruisers but I think they were included in the removal). So you had a Japanese force with more firepower that counted at closer range, more experience and doctrinal history at using it, and better rounds (US torpedoes had a lot of problems in the early years of WWII). The US Navy wasn't altogether wrong - the really decisive WWII actions did take place at longer ranges - but it may have been a problem at Savo Island.