Sometimes the "benefits" of big schools are over-hyped.
Just because they're twice the size, doesn't mean they offer twice as many subject options, especially at GCSE and A level.
A lot of them just do "more" of the same thing, i.e. multiple science labs, multiple tech labs, multiple food tech classrooms, all doing the same thing!
Back in my day, it was 6 forms per year. You'd think that would mean six different levels of ability for the staples like Maths and English. No, there was just top, middle and bottom, but done twice, i.e. top middle and bottom of forms A to C then top middle and bottom of forms D to F, so even though six forms, there were only three different classes of ability.
Same happened with French in year 10. Roughly 50 pupils doing French, but instead of a top and bottom group, it was again split into A to C and then D to F, so two groups of equally mixed ability!