Yeah but it was all for the purpose of having sex with her. They simply didn't think she'd actually fuck any of them out of her own volition and so were making this stupid elaborate plan with extra steps. It wasn't about being in control per se, it was about having a fuck with her at all.
They're not happy that they had to share and take turns, but it'd be the same thing if they were "in control". They'd just be fighting between one another over who gets to fuck her first and who gets just sucked.
If you think back to the jacuzzi scene, Susan was the one who was in control there too. She was the one who was picking who she makes out with and all the other actions. They were more than happy with it then as long as it meant they'd get some action with her.
You're wrong. If that was the case, why would Adam suggest that him filming it on his phone, would put him back in control? Yes, the plan was mainly about corrupting Susan, so that she'd have sex with them. But that never involved her being the one in control. They naively assumed she'd be the submissive one, and she'd ultimately do whatever they wanted. And maybe that would have worked, if nobody else was trying to make Susan more sexually open at the same time. What they didn't anticipate, was that Jo was also working to make Susan like her. And since Susan was in on that, it's had a more profound effect on her, and she's started to become sexually confident, in the same way that Jo is.
All along Mike's plan has been that they make Susan believe that she's in control. He tells Adam to be really nice to her, compliment her continuously and help her out. So it's them essentially manipulating her, to ultimately do what they want and that implies control. They're not openly saying they want to have sex with her. She has to believe that it's entirely her own decision. And if Susan was not under anyone else's influence, perhaps it could have worked, the way they anticipated. But Jo was working on her in tandom, and unlike them, she wants Susan to be self confident and in control of her own sexual destiny.
There's a theme all the way through this game, that the women are the ones who are really in control. The men may believe they are, but ultimately they are slaves to their own dicks, and that allows women to be the ones calling the shots.