Pilots trained for carrier missions will allow even an overcrowded carrier to function smoothly, swarming the enemy and vastly improving their effectiveness in naval battles.
原文の説明読めば艦載機の方だと分かる
ちなみに英語wikiの解説でも
Carrier overcrowding: This doctrine reduces the penalty for crowding too many planes on an aircraft carrier.
とあるからやっぱり艦載機過積載ペナ軽減だね