The way I see it is that if they wanted you to be able to fly a 737 they'd ask for a TR or an MCC via OAA on the RYR program (and knowing RYR it wouldn't surprise me if they did require that, but they don't). The sim check, in my eyes, is a way to see your general flying ability, team work and to get involved by asking questions. They don't want to see a withdrawn character who just sits there a nods.
IMO, if they know you've flown a 737 under their SOPs, there is more for them to test you on, they could ask you questions on the 737 which might just catch you out. Oppose that to somebody who done their MCC on a Citation or a TP, there's a less chance to mess up under the enormous pressure you'll be under on the day.
I wouldn't pay 7000 for an MCC or some 737 experience. If you're a worthy pilot, they'll detect it. It' their job. My opinion, no experience in this field.