if there are 100 students applying for a course, surely most of them are going to be pretty similar anyway.
100? A typical RG course that's actually viable will get at least a 1000 applicants.
As someone on another thread who's actually an admissions tutor said, the problem with personal statements is that almost everything people put in them boils down to "I am middle class, and my parents have given me lots of opportunities because they have the time, money and inclination"; if you used personal statements to do admissions you would basically kill any hope of a diverse intake stone dead.
Personal statements from first-in-family applicants from schools with no tradition of sending students to selective universities are often a car crash (I read them prior to doing "one on ones" at applicant visitor days) and if they actually were being used for admission, they would be excluded on that basis alone.
Students from easier backgrounds clearly invest a lot of time in personal statements, get offers on the basis of their sensible A Levels, and thus inadvertently perpetuate the idea that it was the effort on their personal statement wot did it. It's like the myths around secondary admission: people who would have got a place anyway but who did some weird ritual involving chicken entrails tell people it was the chicken strangling that got the place, forgetting that they live next door and have four siblings in the school already.
Get reasonable GCSEs. At the end of Y11 look at prospectuses. Carefully note the A Levels that are required and desirable for the general sort of courses you want to do. Do those A Levels. Come Y13, look at the grades required. Pick courses realistically based on your predicted grades, in places you fancy living in for three years. Visit a few of them to get a sense of the courses and the departments. Apply and get five offers. Work hard for your A Levels. See you in October.