Why'd Cantonese restaurants desire 40,000 BTU for soup?
For a domestic kitchen a few thousand BTU is plenty as you will rarely need to heat more than a few liters of liquid.

In a professional kitchen you might be asked to prepare a 30-litre portion of soup or broth or make 5 kilos of dry pasta at once.

Doing that on a domestic range would take ages and that is not something you want in a kitchen. And with the pasta example it might not even work, you'd never get the water back to boiling within the cooking time, leading to soggy pasta.

Once you switch to simmering you simply dial back the burner, these ranges are usually good at finetuning. Or you could transfer the pan to a quieter area on a smaller burner if you have that in your kitchen.