It's all about the mix. You need some centralized courses to dissipate innovations quickly.
The German Army detected many shortcomings in its 1939 Poland campaign.
The lessons learned (that were mostly about "mistakes of our officers") were compiled and thousands of officers were moved through courses to correct the deficiencies in about half a year.
On the other hand it seems natural to me that soldiers join their unit after periods of courses and train with it for a rather long time before it's again about time to attend schooling for new assignments.
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