I don't think anyone has ever said "Dan likes it" until Dan expressed himself liking it (which he did twice. Maybe thrice?). People do, however, forget that he couldn't just walk off because the financial bound he had with JJK but consistently suggesting he just straight up leave. He did, find a way to get out eventually, but at the time, no.
Despite us knowing, Dan did agree to the terms and conditions and was asked if he has done it before (to which he lied and said yes). So weather he obviously hates it or not, it is unfortunately, consented. Let's say if they signed a paper, Dan would lose the court case (for multiple reasons since he's a guy) due to the document he signed. Anything outside of that would be considered assult since he pretty left the contact. If he chooses to do the deed, it is his freewill.
I think the person wanted to make sure if you're gonna argue, at least use the right terminology.
JJK was rough as hell and it was more like constant r@pe. But just like you said, it was unfortunately transactional, Dan had his own motives to help save his grandma, so he accepted it.
What gets on my nerves is him falling for JKK in the middle of that rough interaction.. it's true that love is blind, and it really happens in real life
+ it's real that some people love to do it rough & violent & that's why they pay for it in sex services already agreed upon

I keep seeing people saying that Dan should leave JK and JK is toxic blah blah. That may be the case if they’re lovers, but they’re not. They’re in a paid relationship guys. Dan is with JK to pay his debt and JK is with Dan for sex. It’s purely transactional rn. Idk why the readers keep jumping the gun and being like “that’s not how you should treat your partner”