I had difficulty with A levels, but this was very much a consequence of the teaching, class sizes, and difficulty of a lot of students in my A level classes. Yes there are schools in which everyone gets top grades, and I would expect in those conditions it is easier for one to achieve top grades oneself. If you happen to be in an inner-London comp then you're gonna find it more difficult however bright you are. Cambridge is very different. I managed to do ok, and I could probably do any GCSE now in 2 days and any A level in 2 weeks (apart from languages of course). That's because I now have those skills. It doesn't mean that A levels are easy.