Well, the main point of the conversation with the fuckboi is that he looked down on gravure, and that’s what bothered Sakura. Maybe Sakura will go back to gravure to prove to the fuckboi that gravure isn’t shit or something like that. Maybe that’s what Mio meant by “proving them wrong”
He looked down the gravature but also associated the sex scene to the gravature image that Sakura had and her agency are against the sex scene because they think she should have the image of a pure girl.
So accepting the scene would make Fuckboi and her agency wrong because it would prove that is capable to do it.And it was Mio's point,she would prove that they are wrong about her.
If she refuses to do nothing would change in her development.It literally would make Sakura stucked in her development
And gravature models does sexual scenes or sex scenes so it literally support the decison to do it.
I think Fumi will be the bait and Sakura will go all the way.Because Fumi has Shinobu to stop her and Sakura has no one to stop her(she ignored fuckboi and likely will ignore her agency)