Not every one was surprised by the Zero; Clare Chennault and his Flying Tigers realized their P-40s were no match for the A6M in a turning fight, so they developed tactics that emphasized the Warhawk’s speed and durability; climb high, attack out of the sun (if possible) disengage and re-attack only if conditions were favorable.
Same thing with LCDR Jim Thach, creator of the beam defense maneuver that bears his name. Three months before Pearl Harbor, Thach read a fleet intel bulletin that highlighted the outstanding climb and maneuverability of the Zero. Rather than dismissing it as bunk (as many fighter pilots did), Thach began working on tactics that would give his F4F Wildcat pilots a fighting chance.
As in other example throughout history, the intel was there; unfortunately, a lot of commanders and pilots ignored it and paid with their lives.
Chennault was not surprised because he was over in China fighting the darn thing and Thach developed his tactics after being exposed to the Zero.
However, you are right. The Departments of the Navy and War were both warned about the nature of the opposition - and chose to ignore it. Also, the were complete wedded to concept of daylight bombing by un-escorted bombers and killed tens of thousands of airmen.
I have to wonder what stupide ideas the DoD will used to kill our troops.