Let's make one thing clear from the start: This path is not for everyone. When you embark on this path, you should pursue it stubbornly and ignore everything around it. Then and only then does a really good criminal story emerge. In my game Anna fucks exactly 4 times; during the 3 "contract negotiations" and once John -> with the pistol in her hand!
But I agree with you, if you mix it up, it will be shit.
Are you saying you've only allowed Anna to have sex 4 times in the whole game? If so, you've sent her to Nympho Hell!
By the way, the contract negociations aren't part of the criminal path. The criminal path, is the part of the game connected to Sergey's Gang. So any sex scenes with Sergey, Carl, Michael, Fitzgerald and his brother, the Black Cat Brothel Patron, the prostitute and her customer in the Park, the drug dealer in Season 1, a scene with Benjamin in the alley, plus that scene you mentioned with John. If you want to play the criminal path and nothing else, then you need to include all those scenes.
Plus there are other scenes that could be construed as having a criminal element, even though they're not technically part of the criminal path. The various scenes where Anna prostitutes herself, the two in the Bar, one scene with Lenny, and the escort scenes with Burnfield, because unlike in most of Europe, prostitution is a criminal offence in the USA. Plus the Taxman, he's obviously involved in illegal activities, we just don't know what they are yet. Anyone who has the local police force in his pocket has got to be dodgy.
As far as the contract negociations are concerned. I think they occupy a grey area. What Anna is doing, might be considered unprincipled by some people, but it's not actually illegal. If any crime is being committed, it's not by her, but the other side in the negociations. By accepting sex from her as a sweetener, they are in effect defrauding there own shareholders, because the contract then costs the company more, than it would have done, if they'd negociated strictly by the book.