He with the money has the power.
A Pro-Dom really has no power. She's simply selling herself. Pandering to male sexuality. I find it ironic - the bottom actually is the one in charge cause he's paying and she's doing what he wants. A real Dominant Woman is next to impossible to find. Pro Doms are simply women selling sex for money.
Cuckolding is very similar. I read the article posted by Gen and it is interesting because the couple in question are clearly using their Bull for their own sexual pleasure. Sure, he gets to fuck a good looking woman, but really, he's just a monkey doing what he's told. He's simply a prop in their sexual world. Any man who allows himself to be cuckolded WANTS to be cuckolded and therefore - really isn't a cuckold now is he? (I guess it's a fantasy situation.)
I understand the fetish, I find it exciting even - the "hot slut wife", but really, Can I truly be a cuck if it is what I want?
As to financial domination - that's just silly and if any man is so stupiid as to partake in it, then good for her. (I say that since I clearly see no sexual reward for my hard earned money.)
The thing about power play is that it is just that, power
play. Assuming it is taking place among consenting adults (as it should be), I would suggest that rather than one partner being the "true" dominant one or the one with the "real" power, both partners are equally in power as nothing that will take place will go beyond what both partner have initially consented to. I would also suggest that both the dominant and submissive partners are getting what they want/desire/need out of it, including paid-for power exchange play. For instance, the pro-domme may be playing according to the desires of the sub client paying for her time, but both are getting what they want out of this transaction: he's getting his rocks off, and she's getting paid for it. The good pro-dommes are also usually experienced lifestylers who enjoy the play beyond the financial compensation.
Similarly, and assuming that everyone in a cuckolding scenario is a fully informed and consentual party, I would suggest that they all get what they want out of it, and no one is actually more or less in power than the other. Yes, in the example above, the bull can be seen as merely a prop for the couple's fantasy. But from his perspective, if he's getting what he wants out of it, who cares if he's their prop? Same goes as you suggested for the cuck: he's only a cuck because he wants to and gets off of it.
Basically, as long as every participant in a power exchange play is free to walk away at any time, no one is ever in "real" power over anyone else. But that's also why it's possible for those involved to eroticize the power exchange. "Slavery" is hot as long as it's consentual. There's nothing hot about real slavery.