I mean, there's no reason why the player should have agency on the NTR route (you don't even have agency on the NTS route, so...)
This is game - not an actual NTR situation. Up to this point player was always getting a chance to affect the story. Only in this case suddenly everything is decided for player - MC suddenly is ok with Mia filming other people having sex - and suddenly it leads to Mia sucking another dick, because she is not sure if her blowjob skills are good enough. And Lisa decides to make a photo of that (and Mia is somehow ok and not aware of that?) - and send it to MC. So Mia and MC breaks up and NTR route is over in next update? They make up, while MC is now ok with Mia sucking another dick, because he was bad boyfriend?
Bad boyfriend was plausible reason for Mia to be more accepting to have a "relationship" with Luke, at least. But wanting to improve her dick sucking? I don't know about that. Of course she could be aroused after seeing what Lisa is doing, but Mia didn't think of just going to look for Luke in this case?
I don't mind this scene being in game - many people enjoy it (as seen by the comments) - but it being unavoidable is a dealbreaker for me.