I stand to be corrected. But I don’t understand having to change the temperature no matter how hot or cold it is. It’s thermostatically controlled so it will heat the car up as fast as it can to the temperature you have set it to if you set the temperature to 21c it will heat as fast as it can to 21c. You turning the temperature to 30c will make no difference to the heating time. Unless you want to heat your interior to 30c.
Am I wrong???
Don't forget that the temperature will be different in different parts of the car. People on one side may be in sunshine and so want a cooler temp, while those in the rear are often lagging behind, hence the reason why some cars have 2 or even 3 zone control. Then you might have passengers who have different comfort levels. Lots of reasons for changing the temp and other settings such as directing all the air to the screen, face, or feet on occasions.
Also, even assuming that the temp control in the car doesn't use proportional control, where the heating/cooling is reduced as the set temp is approached, I think you are missing the point about the difference between the air temp in the car vs body temp/comfort.
If I'm chilled to the bone, my personal body temperature and comfort will be more quickly restored by heating the car, initially, above 21c and then dailing it back down when I thaw out. The converse is true when cooling is needed.
It's not about how long it takes the heating/cooling system to decide the air in the car has reached the set temp, it's about how long it takes me to reach my body temp/comfort zone. As I said, I think that is best achieved by setting a higher/lower temp and fan speed to start with and then reducing/increasing the set temp as I get comfortable. On the coldest mornings I even start with re-circ turned on as that also speeds up heating the car, then I switch it off to restore fresh air.
If you are happy leaving the temp and other controls always at the same settings, that is your choice, but it still doesn't alter the concerns with touch controls for those who need or choose to use them.