I disagree... the POTUS (and SecDef) should absolutely have military experience.
It's like the equivalent of your new LT being some cherry fuck out of ROTC/OCS that has zero experience in anything, and getting a guy that spent 6 years enlisted and went green-to-gold.
The latter guy will have a much better idea of how to utilize the assets available to him in a more efficient way to achieve a better outcome, because he actually understands their capabilities and value.