Although, one point that does perhaps indicate mathematics is one of the harder degrees, is that ultimately to do well on pretty much any degree you just need to put in the work. Most people could get a first if they worked hard. This is true in maths (and other subjects like physics) but it's only true up until a point. Some people literally never fully appreciate a theorem or abstract idea in mathematics and no amount of hard work gets them to that 'eureka' moment with some of the work. I know this is true for other essay subjects as well, but mathematics isn't bound by the English language, or really anything for that matter, there's areas of mathematics which only a few people in the world properly understand, it's quite literally limitless to a creative mind. Some people find beauty and deep meaning in artwork, music and books (and I do as well) but, in my opinion, it doesn't come close to the creativity and pure genius of some of the work of the best-known mathematicians over the last few centuries. Maths is just completely unparalleled at this high level, in my eyes. It's not exactly relevant to the thread though as it's mostly irrelevant to a degree
(but does, perhaps, give some insight into why people often say a maths degree is the 'hardest' degree, right or wrong).