I do find it laughable that people who spend 36 hours or less a week in an office complain about their hours and/or being worn out. I can understand why someone like a teacher would be drained but not someone in an office job.
Not that laughable as it depends on the work people are doing in an office. Even sticking to my core hours, it can be an intense and draining day and all of it in an office. Location and hours of work are not a benchmark of whether or not someone can be worn out from work.
I know your circumstances are different, but I think in places I've worked, the in early out late culture is a bad measure of an employee's suitability or effectiveness. I generally stick to my hours because I want to get home to my family. Every year my objectives are met, budgets gained, clients happy. Every year I get a comment on how it's noticed I don't stay late. Every year they get the same response about them engaging in auto-copulation.
A colleague continually misses deadlines, sometimes by wholly unacceptable amounts, but at least they're here until 7 each day, that's all that counts. Apart from the cost of electricity and everything for all those who aren't that efficient or engage in the charade of being here late.
As I said, I know your circumstances are different, but you can be drained from office work, it depends on the work. Even the simplest work can be draining if it is never ending and you can never meet unrealistic goals. And you happened to have opened up a very sore point for me throughout my career