This sounds about right, using sugar as a spice and to balance and activate other flavors. By habit my mother always put a dash of sugar in her cooking, whether Cantonese or others, so I do too. Any dish with sauce or gravy, pasta or stew, I do this, along with umami and other flavors. Sugar balances many flavor, takes the edge off.
I know next to nothing about Thai cooking but I do know a key is balancing heat/spice with sour and sweet.
Otherwise, I dislike overly sweet dish like sweet and sour dishes. Personal gripe is Cantonese tomato beef dishes. On the West Coast it’s usually overly sweet, ketchup-y. Chicago style is savory, balancing the sweet of good tomatoes with beef and black bean and garlic.
Generally overly sweet Cantonese dishes like sweet and sour are called white people food. Sugar is one of the dominant additives in American prepared foods after salt. Sweeteners are often at or near the top of the ingredients list.
Desserts are also an area of less sweet in Asian cuisines. Prime example is a cake from a Cantonese bakery will be significantly less sweet, usually with fruit and a light dairy topping. If something is sweet it’s usually natural, like red bean dessert soup.
Side note: with the rise in the use of sugar in Asia comes the rise in obesity and diabetes.
