Let me answer your question with a question.
Tell me, who has the real power when one is gagged and tied down, on their knees getting fucked, fingered and spanked and the other one gets to do the fucking, fingering and spanking?
I have personally found that who is in charge is often a point of contention, even in a M/s relationship, especially in one where the submissive has as of yet to fully surrender in their heart to the will of a dominant and even then some dominants wish to allow one to retain as much of their spirt as possible, prolonging the dynamic in many ways, with several different degrees of surrender being involved.
"Beware la kajira lest it is you who ends up enthralled at her feet instead."
In some ways its a constantly changing dynamic, a two way street if you will. There is a certian degree of give and take, in power exchange.
We can spout all the window dressings of "equality" of this and that we wish to make us feel all fluffy about the the topic of "true power" and where it resides but it wont change a thing when it comes down to the brass tacks in actual practice; despite the giving and taking that occurs. Even the sacred holy grail of the "safe word" will not allways save one, the dominant ultimately is the one who decides if such is to be honored in reality and even if it's allowed the sub, there are situations in which the use of them isnt allways feasible.
As for ending relationships, well, anyone can and allready does do that, regardless of title within the kink community, at least in developed societies. (Unless being held actual prisoner and well then, whatever asshole is doing the holding needs to go to jail) The majority of us all are denziens of a society in which the rule of law is clear on this and yes even those of us who are slaves know this and will leave your ass if you go too far.
Choose to submit and you place yourself at risk to some extent. There will be times when you are completely at the mercy of another.
Tell me , who has the real power then?