I don't think it's that people don't believe in the word, "dominance." It's that it is thought that domestic dogs don't operate within a consistent hierarchy. What we see, when we see a pattern in behavior by one dog or another, such as you describe is often a learned behavior, learned by association...history, rather than due to a linear hierarchy operating or one dog seeking a step up the social ladder into a particular rank.
It sounds like Kim is a bully. A real leader, one who guides others is one who controls resources, not one who throws his or her weight around or behaves in a forcible or aggressive way. This kind of behavior is often the product of insecurity rather than confidence. And what you see might be the weaker dog giving into the bullying simultaneously or just before he thinks he's going to be attacked or knocked into. We can miss signals that dogs give off too, as they can be very subtle. Usually it's the weaker dog appeasing the aggressor in order to deflect further conflict and there are very subtle signals that a lot of people miss. Some dogs ignore other dogs' signals. The other dogs may be giving a calming signal and perhaps Kim is not recognizing and respecting them...and continues on, obliviously with her forceful ways.
Personally, I wouldn't tolerate a dog body slamming and pinning another dog if it weren't in play. (which I have never seen in all my years) Even if the weaker dog submitted voluntarily first... I wouldn't let that bullying go that far, to the point where the other dog is cowering with it's tail between it's legs and practically peeing himself. I don't let pushy behavior be reinforced because I, as the human do not go for it. I don't believe in letting my dogs call the shots. Smaller matters, small warning growls to communicate and observing if the other one is respecting that, so a situation is resolved easily is one thing. Letting it get to the point of engaging in outright bullying behavior, is another.