In terms of Joan's choice. It was a choice, but the best of a number bad choices - so it was coercion too.
As background, Joan was born in an era where, at least in the environment she was in - the ad business - she had to use her sexuality to get ahead. I mean, she had a choice, but the choice was to stay in the secretarial pool. If she wanted to get ahead even as far as she had, her only choice was to use her sexuality on occasion including sleeping with powerful men. For that matter her marriage to Dr. Rapey was based on looking for a good catch. And note that when she announced her engagement Peggy commented (completely without irony) that he sounded like a "real catch". (Of course nobody but Joan and Dr. Rapey knew he was Dr. Rapey. And probably Dr. Rapey never thought of it as rape, and it took Joan years to realize that rape was what it was. The term "Date Rape" was not invented at the time. )
And she though she had moved beyond needing to use her sexuality any more. But note that in spite of her talents, she never got beyond office manager. Every other major character we saw move at least once. Joan was still in the same apartment. Neither her sexuality nor her talents and skills (which really qualified her for Lane's job) got her beyond that.
And then she hears about the offer, and that everyone is considering it. When push comes to shove, the men running the firm still see her as a body to trade. And they will blame her for losing Jaguar if she does not make, as will most of the people in the firm. And if she wants to be a position where this can never happen again, she needs to make that trade one last time - but on her terms.
It is not empowering. It is horrible and disgusts her. But under the circumstances she sees it as the best choice she can make. A horrible way out of a trap.
At least that is my take.