No, BTM, DS didn't look at Sociology any more carefully than he looked at Psychology. Apart from PE and Biology (which he's pretty clear about as regards course content etc) he has pretty much gone "umm, that sounds nice, yeah" and that's it. He knows absolutely nothing about what's involved in Psychology A level, and refuses to do any reading or research into it; he was forced to choose a 4th subject, and that was the least worst option. Personally, I think he will hate it.
Film Studies he really fancies because there's a fair amount of actual practical film-making included. This fits with his fantasy career of being a famous YouTuber. 
Yes, it also involves interpretation/essays (like Eng Lit, only films instead of books, obv), but he seems to think this will be OK. In truth, he has never liked reading (no son of mine), so he might find a visual media easier to interpret and analyse. I hope.
He's now moaning about PE, because he doesn't want to play football any more. 
Is he good at Maths? Not really. He'll get a B or C. If he doesn't get a B, the college won't let him do the Biology A level anyway.
He rejects the whole concept of BTECs because he's "better at exams than coursework". Won't contemplate anything vocational, as he's not interested, and is about as practical as his father a chocolate teapot.
Favourite subject? Doesn't have one. Doesn't really want to do anything next year, but that's not an option.
Honestly, it has been a nightmare getting him to engage in the whole process. On DH's recommendation, I'm giving him a few days to decompress after exams, then he will need to give it some serious thought.