I'm not trying to be a contrarian to everything you're saying, but...
Actually that second video impressed me the most. A human torso is only so deep, and I think I just as soon have a large pattern like that, and that stays embedded in the attacker. Minimal exit wounds to me means maximal force of the blast absorbed by the attacker's body, and minimal chance of drywall penetration into other rooms (or neighbors' units).
And I'm pretty hesitant to assign much meaning to ballistics gel videos, beyond the cool fireworks and lavalamp-like visual aspects. As implored in the old video game Doom when you pick up the chainsaw weapon: Find some meat!. Here's one, of lowly birdshot making a hamburger wound in a mock assailant.
Granted that's at only 10', but my intended defense chokepoint, the long part of my staircase, is 12' from upper to lower landing, which is right around the same as this vid's 24" muzzle plus 10' distance from the muzzle. You might have a bigger house, and no neighbors, so YMMV.
Now what if the attacker is superman on PCP, you might wonder. If a shotgun can hold four shots, I probably do have four shots since each would probably blast the guy back down the stairs after each charge up them. I suppose for the first I'd aim for the stomach, the next one in the genitals, and the one after that in the face. And then maybe your slug as the fourth. And then planning on spending the rest of my life in prison, I guess. Except I'd rather die than be in prison, so I guess I'd just let him get me then, at that point.
Maybe the fourth your 00 buckshot, to one of his knees. After all that he won't be able to walk or see, so I should be able to get away.
But more realistically, to the ordinary intruder (and potentially partner(s) in crime), the kerchunk will cause him(/them) to not even want to think about going upstairs, if it means hazarding close-range shotgun blasts in a narrow corridor with nowhere to go or hide.
Now if bad guy(s) is armed and decides to shoot through the floor at my estimated location... Install steel plating under the drywall of the corner I'd shoot around, and under the carpet where I'd stand? (This home warfare thing is crazy.)