This is nonsense. Physics and Chemistry are wholly separate and very different subjects, and medicine is completely unrelated to the others. Beyond that, engineering covers a vast array of subjects, some of which overlap with other areas (Materials and CS, which you have decided to list separately, but not the former). You've indicated no metrics by which to rank them, and so this is just completely arbitrary.
In terms of your later comment about "academic difficulty", Mathematics is by far and away the subject with the greatest potential for intellectual challenge. Medicine isn't "difficult" in this sense, it just has high barriers to entry due to limited spaces imposed by the government, and a large quantity of information to cover. While some is more or less difficult, most medics wouldn't be able to pursue a Mathematics degree, whereas most Mathematicians, if so inclined and had taken the relevant subjects, would be able to cope with the intellectual demands of a Medicine degree (although perhaps not the emotional demands and amount of time required to devote to it).
For reference, my Physics and Maths friends referred to Engineering (my former subject) as "Arts and Crafts", which is somewhat indicative of where it lies in terms of absolute intellectual difficulty in your "list". Like Medicine, the challenge is primarily due to it's popularity (as it more directly leads to well paid positions afterwards) creating barriers to entry, and a broader workload involved - although this varies a fair bit between the disciplines anyway.
However this is irrelevant as there is no "absolute intellectual difficulty", since there will always be exceptions to any given case and knowledge can't be fundamentally quantified as such. One might argue Fine Art is the hardest degree, as it's almost entirely self driven, almost impossible to quantify (and yet you do get quantified and given a degree classification) and since it's so interpretive it is necessarily harder to achieve e.g. a first class result as there isn't simply a "right or wrong" answer - this also applies to say, Philosophy. It's well documented that "arts" subjects at Oxbridge tend to have lower average results than STEM subjects as a result of this higher difficulty to get the top marks, as there is much greater leeway in how the examiners assign marks. Does this make the subjects "harder"? More "intellectually/academically difficult"? Not necessarily, obviously.