The questions are the same level of difficulty because they have to assess at the same level.
EdExcel is the easiest exam board for maths just because there are so many people taking it. This means that there are lots of resources readily available. I do AQA and D2, M3, M4, M5, S3, S4 don't have textbooks. FP2, FP3 and FP4 do have textbooks produced by AQA, but they are sometimes very difficult to follow and learn from.