To Sento only,
I don't disagree with what you wrote about which knuckles to use, but the reason I phrased it the way I did is that I don't know the OP's background/style. I met some Shorinji Kempo guys who were adamant that a vertical fist with a first two knuckle landing was the only "true way". They cited bio mechanics, ki theory, other stuff. They also talked a bunch about "concussive" force vs impact. A couple of them could bang. I have worked with some Okinawan Karate stylists who were were of the opinion that most of the force should go into the first knuckle, and that the twist/transition from vertical to horizontal needs to happen after contact (sort of screwing into the target). They cited "penetration", bio mechanics, energy, etc. A couple of those guys could bang.
Pretty much any possible landing/alignment seems to have someone talking about how it is best, and they all claim to have mechanical/bio mechanical advantage. I also know several guys who have knocked out more guys than I have fought, in "street" fights so all bare knuckle, who pay zero attention to this stuff and never injured themselves.
I have also noticed the fist alignment arguments seem to incite purse swinging like few other topics so even though I think it's important, I just don't wade into it unless it is specifically asked. Because I might accidentally start a religious war.
To the OP,
Following Sento's advice about what knuckles to land with would be rational.
RE the Rich Ryan vid
I like that clip a lot. It is one of the few simple/gross movement pattern techniques that actually is, and also doesn't suck. I really like how he emphasizes that the "speed" strike is most likely to buy you an opportunity and isn't some "better" than boxing method that he can teach in a weekend. He even mentions that it forms a template for improvement. That honesty shouldn't be rare in self defense seminar material(as opposed to long term training), but it is.
My favorite part though is at the end. One of the shots you can see he puts his body into. It isn't big, but it just looks like most of him is going in the direction of the strike, maybe only an inch or two. The target is floppy enough that the power difference might get missed, but that kind of technique/efficiency is just a joy to see. I would love to make that the example for people starting out.
"Look at how he shifts damn near ALL of his mass into this strike. No wind up. No grunting. Just a clean, powerful collision that he wins. Make that efficiency the goal, no matter if it takes you 2 years or 20 to get there."
Great post. Dempsey's method always seemed to me that it relied a lot on being ready to hit hard for its "defense". If we are nerding it up I would point to high guards and two handed swords as the fencing equivalent. A huge part of the defense is that you have to deal with a serious threat moving in. Not so much slick, as something is coming that is going to own a given line/angle and if you get clipped your attack gets fucked up. The more polished, off the back foot, style is closer to a "Spanish circle" where the goal is that any attack walks into a threat or gets pulled into a vulnerable position.
If those analogies work than the strengths of the "Dempsy"/offensive oriented defense is
-Much less dependent on having to read an opponent. If they move in, take the line and hit them, if they don't take the line and hit them.
-If you can't fire (out of position, can't recover fast enough, etc.) you get fucking wrecked.
-If you don't have credible power than the "threat" isn't and you get run over, rag dolled, and raped.
The more polished method's strengths
-Less dependent on having huge power
-If footwork is compromised shit gets real. In theory the Spanish school stuff is perfect. In practice uneven ground, fatigue, a slip can make it go to hell in a hand basket. This is far less of a an issue in a clean ring, or dueling circle than say a battle field.
-It is much more "diagnostic" intensive. So if you bite on a feint or mistake one attack for another than the "RIGHT" counter might be wrong. Blood in the eyes, or sweat for that matter, can make this a bitch.
Personally I like watching the latter more, but that is preference.