Since some very experienced chicken keepers already responded to your question with nearly opposite points of view, I watched your video several times to be sure of what I thought I was seeing. It looked to me that the submissive hen was trying to get away from the dominant hen, got caught in a corner, submitted by squatting, the dominant hen mounted her, & the submissive hen did Not appreciate it. The submissive hen then squawked and struggled to get free again before realizing she could not escape from the hen on top, so re-submitted and quit struggling.
Ive only ever had the above behavior occur in same-sex flocks. If I see it with hens, I add a male(s) in with the flock and the behavior has ceased every time. The same dominating behavior can occur in bachelor flocks, and males are often quite rougher and more aggressive in their "domination."
So yes it's domination. but by the fact you included so many question and exclamation marks in your thread title, the sight clearly disturbed you. And I gotta say it, when referring to the "R" word re humans, that crime is said to be about domination, not sex. So umm. Call it domination or call it mating, the appearance is the same. I think it is highly unlikely the dominating hen will physically hurt your favorite hen; you just have to decide if you are willing to tolerate it or take steps to correct it.