So yeah either they could make maths a-level much more rigorous and add a lot more content so that people doing maths degrees actually know what a complex number is before going to uni, or have 2 a-levels. Maths a-level isn't just for people who really love maths, it's for people who need maths in the degree they want to study or people who just want a logical and quantitative subject. It would be unfair on the people less committed to maths, if you doubled the amount of content in a-level maths so that the people committed to studying a highly mathematical degree will be adequately prepared for their course. And before you suggest that unis should just teach the further maths stuff at uni, maths degrees at top unis are packed with content as it is and it's a waste of time to spend the first term going over basic stuff rather than simply jumping into university level topics.