I'm not so sure there's much surprising there. Heavy weights are more effective than light weights?
I think you would see the same for any exercise.
I'm at a loss, though. I have never came across kettlebells over 24KG. I've done swings for high reps with a 50KG DB, though, which is the heaviest i've had access to so I guess I probably can't comment much. I've done swings with two 24KG kettlebells. I also wouldn't invest in one heavy kettlebell. When you get stronger it essentially becomes a waste of money.
I use swings a lot for conditioning. I love any kind of hip hinge. Again I just don't have access to heavy enough kettlebells to run with this idea.
I agree that people who can swing correctly can also deadlift correctly. It's all the same thing - a hip hinge. However i've found it easier to teach people basic deadlift technique first, THEN teach swings, rather than teach swings THEN teach deadlift.
I would actually argue that if you can't deadlift correctly, you won't swing correctly. But this could be a chicken and egg situation, really, and can depend largely on your approach to training people.
I don't like the squat swing, which is what you see the masses who have been brainwashed by the kettlebell fad doing most of the time. BTW, I really like kettlebells, and I love a lot of the traditional kettlebell movements, I just don't think they are a be all and end all (big fad in my gym right now, hence the slight rant).
I also believe deadlifts can be trained regularly without being overly taxing if programmed and performed right. Frequent, heavy, rounded back deadlifts will definitely "take more than they give back", though, but that's not what I recommend.
I have had a lot of good progress with dynamic effort deadlifts, though. I like DE deadlifts for increasing deadlift due to specificity, too, which you don't get as much with swings (if the goal is a bigger deadlift). I like the opportunity via speed work to master technique with a lighter weight. If I have a deadlifter slow off the floor, I can normally get them stronger with one 4-week wave of speed deadlifts (quite often i'll program it from a deficit, too). It's been my first port of call for this problem for years now because it works time and time again. I also make people grip with double over hand until the weight gets heavy, meaning when they do DE deadlifts, they grip double over hand because it's a light weight, but normally with more weight than you would kettlebell swing, so I can throw the grip point right back in that case. I would say having to bring the bar to a halt in a DE deadlift, for the purpose of increasing ones deadlift, is a PRO and not a con of DE deadlifts. This really comes down to why you are doing what you are doing, though.
I just think swings are a ballistic deadlift. I love them and use them a lot (with DB's, though), just not for the same reasons. I also love DE deadlift for specific situations. I don't think one needs to throw out the other.
"swings and slams" are one of my go-to conditioners. 15 swings, 15 (med ball) slams, repeat until you hate you life.
The "swings vs DE deadlift" issue reminds of "Dimmel deadlifts" which is like almost like a ballistic RDL.
Good food for thought...