The OP has forgotten that Japan's defence strategy is different from the rest of the World. Geography has made the Japanese archipelago an ideal place for some in-depth defence like good SAM radar coverage and Long range Air defence. I mean it takes just an couple of mk.3 Patriots and AWACS with newer generation of X-band radar (design to track Ballistic Missiles and their coordinates) to successful defence the Home Islands. No doubt the Japanese Air Force is lacking behind other Asian rim nation. I doubt JSAF could successful out compete S Korean Air force with their superior F-15K. But Japan can (and judging by current affairs, they will..) easily modernize their aviation fleet from 4th generation to 4.5 gen and 5th gen fighters. 10 F-15J will be used an testbed for an radically new ASEA Radar, 3D liquid Displays and HUD with 'look, lock and shot' master slave systems (like the Israeli F-16I sufa that uses master slave technology to control the Paythoon 5 IR missles at visual/BVR range).
Japan's real sword is the AA/AAD of the JMSDF. Long range Aegis radar and JMSDF ships like the Atago that has 90 VLS to carry SM-3