Not a maths teacher, but I did a maths degree, as did dd1 who's just finished. So this is entirely anecdotal, and opinion.
GCSE: Yes, I think it now is harder to get the top mark. The GCSE papers I did were easy, and the grade boundaries weren't that high either. I'd have expected to get 100% on any paper I did, and I used to do practice ones in about half an hour without really concentrating. I did the maths early as did all my set and only a couple didn't get an A (top) grade.
The new GCSEs look harder to me because they have deliberately put questions in for the level 9 students, and some of the things that were on the syllabus for A-level when I did it are now on the GCSE.
I suppose those perhaps the question is whether it's harder to get a grade 7 now as an A back when I did it, and I really can't answer that one.
A-levels a few thoughts:
I did maths (and further) A-level in 1994. I would have expected to get 100% on the single maths and on the pure further papers. The single maths papers I could complete in just over an hour-they were 3 hour papers, and that was without me trying to rush as two hours sitting and checking was dead boring.
We did practice papers for years back, and although there was a clear difference in difficulty when you compared the papers from the O-level cohorts to the GCSE cohorts, I didn't find any A-level papers that I couldn't do and get pretty much full marks on.
My brother did maths and further four years later when modular came in. He wasn't as good as me at maths, but reckoned to be close. There were two things that I noticed. One being that he was totally thrown by using a method from a different module. He could not combine them at all.
The other thing was he commented that papers from my year were totally inaccessible to his year. He (and the others) tried them and weren't managing to even attempt a lot of questions because they didn't know where to start. I had a look and saw that his papers were completely leading them through the longer questions. Whereas I might have had a question that said: Solve this integration.
His would say: Show that f(x) = g(x) using this method. Now using that show this bit and then show that bit. Then finally using this show that integrate f(x) dx = answer.
So they didn't have to think for themselves which way to do it as long as they could repeat the method. You could say that means that it's testing the maths rather than working out which method, but I'd argue that part of the maths is working out which method, and it also helps with understanding having to work out which method is best.
Anyway, fast forward to when dd did it:
When I first saw what she was doing I thought it was harder, and I didn't know where to start on a lot of the questions. But when I started looking at it, I found that it was a mixture of me having forgotten what was at the tips of my fingertips when I did A-levels and methods/names having changed. I'm reasonably confident that if I put my head down and went back over it, I could get back up to doing it fairly quickly. Whenever dd did ask for help, although I normally had to read up on it, I could do the questions fairly easily and show her despite not having done it for 20 years.
Dd also could do my era papers, with a few queries about names/methods that have changed.
I think sometimes the name changes make them see more inaccessible. I remember one parents evening, the teacher saying that "circle theorem" was something a lot of them struggled with. I sat there thinking "wow! Circle theory was something I found really difficult in the first year of my degree". When I got home I discovered it was what I'd called "angles in a circle".
What I do think is harder now is the length of the papers, because they've got 3x 2 hour papers, and they looked more questions too to me. Dd didn't always finish the papers, and I do admit she's a slow worker, but they certainly aren't going to get anyone finishing in 1/3 of the time like me. I'd reckon I would have finished, but not necessarily had much spare time for checking or correcting. And that does make a huge difference. It means when you know a question hasn't come out right you have to make decisions to check what's wrong or move on. You are less likely to pick up errors and you've also got a panicky feel as time goes on and you're still working.
So my conclusion is that they did get easier, possibly a lot easier, but now I think the difficulty level is similar to when I did it, but the timing makes them a bit harder.
And as for degree, dd's specialism in maths was very different to mine, but I'd say what she did in the first year was definitely comparable to what I did. So from that I'd assume A-levels are similar level.
The difference is that she had to pass all her exams with 40% whereas I only had to pass overall. And as I was very one sided and algebra (university style) and analysis were totally a closed book to me (interestingly dd found the same subjects hardest, which i hadn't told her), then I'm not totally sure I'd have passed overall. I got nearly half my marks on one paper that I was particularly good at. But I'd effectively ignored the subjects I couldn't do and concentrated on those I could; dd didn't have that luxury. We got the same degree level, but I think she actually had it tougher than me and did better.