I know nothing about St Helens.
I have an acquaintance with a dd at RMS. She was sent there because it was very important to her father that she went to a school which was prestigious but she had no chance of getting in to any of the other local indies (this is according to her mother; I don't know the child at all). Her siblings are all at very academic indies.
The mum is reasonably happy with the school. I think there are a lot of exceptionally wealthy families there. Her child has to get a taxi there and it's a 70-90 minute journey each way. I do not think the mum thinks it is worth that (or the amount her ex pays for it) but then few schools are going to be worth that.
I once heard someone saying that it attracted the clotted cream of society's girls (extremely rich and extremely th**k - not my words, don't judge

) but that was a few years ago (my grandma lives half a mile from the school so used to know staff etc there) and it sounds from what G55 says as though there may be changes happening?