I like Doug Marcaida. I also like what he and the other guy are bringing up: going to the ground is a fast and effective way to gain distance from an opponent and make it more difficult for him to attack you.
However, what I wish they brought up is the very real possibility that almost no one ever brings up with these types of drills. Just because you stabbed or hacked a guy with a blade – it does not mean the fight is over. Far from it.
Keep in mind this is true for blades as well as guns. In times past, it was quite common on the battle field for a fighter to stab or hack a guy AFTER he himself had already been mortally run through. You are fighting for your life after all and you are already pretty close. This phenomenon was so common that certain fighting systems attempt to mitigate this possibility with slash or cut-through type moves so the attacker retains his weapon and its not stuck in the other guy.
Now bring things to the modern era. Yes, an attacker on the street might get the drop on a cop, guard, or soldier (hello Palestine) with a blade a la the 21-foot-rule, but the chances of S.A.D. (Self Assured Destruction) are high. Cop gets stabbed and then mag dumps. At grappling distances each bullet is almost sure to connect and with maximum kinetic energy. If the guy’s gun gets out then the blade wielding attacker would be lucky if his target eventually dies – forget about himself surviving the fight. One hack/stab vs. 17 rounds of 9mm?
And if said target has an automatic holster like here:
Then the 21-foot-rule turns into the 10-foot-rule. I believe there are times when melee weapons can beat firearms, but as the kids would say, “I’m just keeping it real.”