The Korean War is a good example of top generals and leaders not being the type of leaders we needed to fight a war. And this was only five years after WWII when we had some of the fightenist generals in history. Too many officers who worked on general staffs during WWII and had very little combat experience above battalion or regimental level. Too many officers that were too old to lead combat troops at the division or lower level. Too many political officers chosen for command because they were someone's favorites. It wasn't until they were weeded out that we started pushing the N. Koreans back into N. Korea.
I can only remember the jist, but Marshall went to Roosevelt at the beginning of WWII, but a few years before we entered, and said that although fine men, he need to cashier half of the 0-5’s and up. Roosevelt gave him permission. Even with this the Army still had too many ‘old’ guys.
German reviews of American leadership gave good marks to small unit leaders and to high Generals but was very critical of the quality of division level officers.