This piece hit hard. It’s strange how something so invisible to most of us is simultaneously one of the most complex, tightly-coupled systems running in the background of daily life.
It seems rather non-complex, and I think it has to be, so it can be robust and offer room for errors etc.
It is the details of actually making it work that raise the complexity levels and/or kill you if you don't get them right.
Remember: a decision that in the abstract with infinite thinking time is easy can be extremely stressful when it has to be made in seconds in real time and getting it slightly wrong will potentially cause a catastrophe. And ATC has to keep doing this throughout their entire work shift.
If they screw up, the pilot dies.