How we've learned to use and developed UAV's, MRAPs, anti-IED tactics, etc.
Use it or lose it.
You are absolutely correct.
In the absence of war, military will award promotions based on things other than performance on the battlefield. Many years of such promotions will finely hone a military into a non-fighting institution.
My mother used to go one step further with her saying that war is required to keep society from turning strange.
Without any taste of a struggle for survival, people turn to frivolous endeavors and become increasingly shallow and silly.