One of the comments hit the nail on the head. If you didn't fail an exercise or drill once in a while, it's not challenging enough. If you simply fire officers that fail, you are not providing training. You're incentivizing exercise/drills over real world performance.
Outside entities should provide a variety of conditions that the security forces would have to confront. Not every scenario has to be a complete victory. What would happen if the Dakota NG lost its marbles and had a single tank as support of a company of infantry. Or arty. Winning might be surviving long enough to bring in reinforcements, or accurately identify the forces in play and getting that information to higher. Goes the USAF folks know how to rush it up the chain to NMCC ? Does NMCC know how to quickly mobilize a response force?
At that kind of high level, you rarely get creative useful drills. You tend to get kabuki theater, intended to prove that the system works perfectly. Gods help you if you have a multiple branch exercise that fails to reach every single objective in less than perfect form, on paper. Reality is significantly less important. I know, the politics. The MSM will make out good training to be the most horrible thing ever. "We had excellent realistic training of Security Detachment Alpha Bravo Charlie. They made some mistakes, but learned a lot in the AARs and improved their future standards" becomes "NUCLEAR WEAPONS UNSECURE!!! ZOMG!!"