Mise en place is a useful mental model for everyday activities, but I don't think the author gave a good example in the post.

I don't think intensity or difficulty is the key differentiator between preparation and the actual work. To me, it's mainly about separating tedious and repetitive tasks from the ones that require attention and creativity.

Prep work means that you perform something that you have done many-many times before and it feels automatic. Prep can be also harder and more intense in many ways than the actual work itself.