Actually, this scene bugged me for several reasons. First, no way she takes all of MC that easy. She's only been penetrated once, and it was only part way, and she was drunk. She's displayed that she's uncomfortable, emotionally and physically, with penetration (see the dildo conversation), and she's in an uncomfortable state in this scene because they are outside and she's very anxious about getting caught. A little lube and some encouragement does not fix all of that so easily on a regular sized guy, let alone what MC's packing. Not only does that make it hard to believe she could do it, but I doubt she'd be doing it so easily and without any signs of discomfort. It's too fast a turn around, IMO.
Second, Maya said several times that, even if she were able to have sex with MC, she wouldn't want to film and use it because it'd make her feel like a prostitute. That's where the "fake it with dildos" plan came from, which is exactly what they do (successfully) if you aren't on the M&J path. Deciding to just do this anyway didn't ring true to me.
And lastly -- and this one is 100% personal taste -- I don't like the idea that this triad relationship they are trying has its first proper shared sexual encounter like this. Just as a reader, I think a more intimate scene would have been called for, and would have felt truer to Maya & Josy's characters too. Though I'm sure we will eventually get such a scene, I think it's cheapened a bit by this one.
I think we have to look at this from 2 angles. The first is that this is a porn game and therefore, despite things like its good story that make it more than just a regular, run-of-the-mill porn game, it does still follow porn logic a lot of the time and that logic says that Maya can indeed take the MC all the way with little effort. She's also clearly not a virgin and I guess we have Josy and "Mr Dildy" to thank for that (would have been nice if the MC were the one to pop that cherry, though
), so that may account for the lack of discomfort, and yes, he's certainly bigger than average, but again, porn game. ¯\_(ツ)_/¯
Secondly, she was hesitant to do anything too risqué, but that was before Josy arrived, and I think having her there, having her encouragement, allowed Maya to be more bold. So she has the encouragement and support of two people she trusts and cares about, plus we saw how encouraging Josy was for Maya to have sex with the MC at the start of the episode, so despite the circumstances, Maya clearly feels braver because of this and I think we're seeing the kind of positive influence Josy can have in bringing out this side of Maya.
As for that scene, I do agree that I would have preferred a more intimate and special moment for this first time, but at the same time, I think it serves a couple of purposes. The first is that it gets the Scavenger Hunt done quickly and easily. They could have taken more time, had a proper threesome, but that's probably something they (by which I mean M&J) would rather do privately, so all they had to do here was make it look legit. Secondly, it gets Maya more comfortable with the idea of sex with the MC since she knows she can take him which means she'll be less nervous and more excited about it the next time. Josy seems to be good at breaking down Maya's inhibitions, and this may have been part of that. Finally, it could make the potential "birthday present" threesome more special because they all got a taste (pun partly intended) of what this relationship can be like, so there could be real desire and passion in it rather than trepidation and uncertainty.