It is not labor-intensive if you want a prompt to work in 80%-90% of cases and humans are good at that. But it is labor-intensive if you want to make it to work

It is not labor-intensive if you want a prompt to work in 80%-90% of cases and humans are good at that. But it is labor-intensive if you want to make it to work at 99%. Then you need to go through many cases and "optimize" the prompt, which is the advantage of optimizer.