The amount of effort needed for this can vary wildly depending on the vehicle, it’s mechanical condition, and the speed it’s being driven at. Some vehicles are more prone to being bothered by wind, or grooves in the road, or require more constant adjustments to maintain lane position.
My tiredness is dependant on the vehicle.
I’ve had cars I’m exhausted from driving just after a 1 hour commute, and I’ve had a luxury sedan I could drive basically indefinitely (once did 3000 miles in 3 days, I didn’t mind it at all).
I wonder if the person you’re replying to previously drive a much less refined car, and would see most of the same benefits even when driving the Tesla manually.
Honestly the second part of their focus, simply being aware of their surroundings, should also be muscle memory for any experienced driver. That’s probably why they find driving so tiring, because they don’t plan ahead enough to keep a peaceful flow, rather than slightly too late scramble to gather information when they have to change lanes or something.