This is absolutely true, but there is a strong counterpoint: You also learn the limits of your own systems and how to operate them most effectively yourself (and better than adversaries can, too).
Just to pick a recent example: Russian air defense in the early stages of the Ukraine war was dismal (more specifically: defense against big, slow drones like Bayraktar), despite having sufficient AA capability "on paper"-- the war allowed them to visibly improve.
I'd expect much more value from validating and improving your equipment and its handling than the actual "cost" of revealing its capabilities to adversaries in almost every conflict.
Just to pick a recent example: Russian air defense in the early stages of the Ukraine war was dismal (more specifically: defense against big, slow drones like Bayraktar), despite having sufficient AA capability "on paper"-- the war allowed them to visibly improve.
I'd expect much more value from validating and improving your equipment and its handling than the actual "cost" of revealing its capabilities to adversaries in almost every conflict.