What changes did the Japanese and Americans make between Midway and the Marianas, and what changes should they have made?
Short answerThe Americans improved air defense and fighter training; Japan most needed to use surviving veteran pilots to strengthen training rather than send inexperienced aircrew into a worsening fight.
NotesThe answer moves from hardware to institutions. The American side refined air defense and trained up fighter strength, while Japan needed to pull surviving veteran pilots into the training system after Midway instead of feeding new aircrew into a fight against increasingly experienced opponents. The Philippine Sea was therefore a pilot-pipeline and command problem as well as a carrier-count problem.