It can be mitigated.
Down does not mean effectively subdued when the opponent is armed with a firearm. Video does not always tell the whole story.
Two factors at play here:
You can still shoot from the ground. The fact that “down and disabled” training is standard practice in LE is a testament to this.
The other is “dead man walking” syndrome. Barring a central nervous system hit, even people with unsurvivable wounds will remain conscious and able to pull a trigger for a few seconds to a few minutes.
Kyle DeFoor’s “timers and switches” analogy (bleeding out vs CNS hits) is applicable here.
Not to mention things look a little different when you are staring down the barrel of a gun.