As I said before, the British have a different way of counting their engagements than the other royals. They always come up with an enormous amount of engagements as they list each and every part of a visit as a seperate engagement.
For example the Danes would list : CP Frederik visited Aarhus this morning to visit a hospital (as 1 event)
In the UK: The Duke of Edinburgh went in the car to Glasgow (1), he was greeted by the mayor (2) after which he spoke to the staff of the hospital (3). He visited some patients (4) and after that he enjoyed lunch in the restaurant of the hospital (5).
I am not saying that the DoE doesn't have a busy life for a man his age, but as the British royals count things like that you can not compare it to the more modest way of counting done by most continental families.
If you/anyone want to see if CP Frederik has more or less engagement than the average royals it would be a start to count how many engagements his continental counterparts have. As most RF's publish their agenda's and count the engagements in a simular way that should not be too difficult. But comparing to the British is not an honest comparison, as said, they cheat
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Still, that doesn't mean that 70 engagements, counting the continental way, is a high amount indeed. Esp. as it also includes things like christenings and such. I share your impression that Frederik does enjoy a lot of free time indeed, more than any other crownprince(ss) of his generation.