That's true, Kingfisher, but they do say that choosing two as facilitating subjects is fine.
Also an extract from the booklet
There are some advanced level subjects which provide suitable preparation
for entry to university generally, but which we do not include within the
facilitating subjects, because there are relatively few degree programmes
where an advanced level qualification in these subjects would be a
requirement for entry. Examples of such subjects include Economics,
Religious Studies and Welsh.
I think Economics would be a fine choice along with Maths, FM and music.
My daughter had decent offers last year from Russel Group universities - her A Level choices were English, Drama and RS(Philosophy and Ethics) , she only did those three through AS and A2, and currently studies English at a non RG uni (first choice, and much preferred option
) Also my son did Geography, RE and Music, and similarly had no problems at all getting offers, from all his choices - again many RG universities there, although he also preferred another uni that wasn't at the time RG, but is now .