This was a special/unexpected situation - one of the other passenger jets declared an emergency and needed to evacuate the passengers onto the ground (there were no free gates to return). The firetruck was on it's way to assist with the emergency.

Nowhere has automated ATC because errors look like this.

Imagine it were 90% automated. Now imagine there's a 3 hour outage of the automated system.

You're left with a bunch of planes in the sky that can't stay there forever, and not enough humans on the ground to manually land them.

Now image the outage is also happening at all airports nearby, preventing planes from diverting.

How do you get the planes out of the sky? Not enough humans to do it manually.

Now imagine the system comes back online. Does it know how to handle a crisis scenario where you have dozens of planes overhead, each about to run out of fuel? Hopefully someone thought of that edge case.

There's exceptions all the time. They turn back because a warning light came on. They saw a deer on the runway, a passenger got up to the bathroom. There's no way that could be automatic, plus they often need atc to look at their jet to see if it's damaged.

My suggestion is to restrict the use of smaller jets like crj and turboprops. I know airports like LaGuardia can't handle the big jets either, but they could reduce the slots and require a jet that holds, say, 150 people or more. This would result in fewer flights per day to some airports, but reduce overall congestion while still serving the same number of passengers.