Personally i think this is a useless discussion. As long as i'm in a D/s relationship or in a scene, there's no question about who has the power.
The fact that i could end both the relationship and/or the scene doesn't mean i have the same amount of power. I only have it if i actually do it, which i won't unless my Master doesn't cross any limits we both have agreed upon. (Accidents or unforeseen occurances aside, like the one time i used my safeword because we played outside and a bee was scrambling over my leg and i'm allergic to beestings.)

Within those limits, he has all the power he wants (and needs) to be a caring Dom.