Name change for personal info.
My simplified understanding is there's two types of hard with learning. Hard to comprehend (thinking hard) and hard to persevere (grafting hard).
Because there are professionals on this thread it would be remiss of me not to qualify my answer with my (more limited education) background also. I didn't want to 'taint' my answers by saying I'm good at maths. But yes, I got A's in maths & further maths just before the change to A2 and did P1-P4 with M1-M4. (I made the combo further maths instead of pure & mechanics as it would look better on ucas for medicine at oxbridge) I was a 'gifted' mathematician but I was also spectacularly lazy like many other 'gifted' students until I failed an intercalated maths degree 4 years later partly because it was a 'stats focused' institution but mostly my laziness and inexperience with failure. But It changed my thinking for the better and made me grow up. I agree with @Sequence you haven't lived until you've really failed (try it you might like it). Ten years later I went back and got a 1st in a maths degree part-time over 2 years (so almost the same challenge as my intercalated). I have also tutored and am a 'reader' for 2 universities so my opinion is based on reflecting back as well as coaching adults.
The two types of hard, thinking vs. grafting often get mixed up until you look at the context and personalities behind why some people including gifted young mathematicians struggle with the step up from GCSE to A-level. I'm reluctant to criticise the maths education professionals but I think their advice here is a bit misleading (hence the confusion on this thread) because it follows the rhetoric of their profession.
Much of the maths national curriculum up to A-Level is arguably 'spiral-learning' (Piaget). So even with the new format, and the input from uni's, and the new material the jump up from GCSE is definitely not bang your head against the wall hard. However, it still is spirit breaking, social life destroying mountain of work hard.
So yes, there is a big step up from GCSE to A-level but I really don't think there will be for YOU as a diligent mature adult learner.
In the age of instant gratification the jump from short exams with short answers to long several-stage answers is THE jump up. Teenagers really struggle with that jump and teachers (who also have other pastoral responsibilities) don't/can't put off their pupils with the cold hard truth which is sometimes...
it wasn't that hard dear you're just a lazy toad
OP as a graduate you should be used to long exams and long answers and most importantly diligence. As a tutor I'm used to dealing with adult learners who want to study instead of have to study. The difference in motivation is key.
My god son's mum got an A in maths at AS which in the end she really didn't need to prepare for her postgrad diploma in stats. She likened multivariate calculus questions to childbirth (specifically the waiting on ward while you dilate from 4-10cm). Long, painful and boring. I actually think she preferred childbirth 