A thali is a plate with a set of small bowls, and the arrangement is not decorative. Each position holds a category, and filling all of them produces a balanced meal structurally rather than by calculation.
The format assigns roles, not dishes
A thali specifies that there will be a grain, a legume preparation, one or two vegetables, something dairy or fermented, something acidic, and often something crisp.
Which specific dish fills each role changes daily and regionally, but the roles themselves stay constant. That is what makes the format portable across an entire subcontinent of different ingredients.
Because the categories are fixed, a cook planning a meal is answering six small questions rather than one large one, and no category gets forgotten.
Nutritional balance falls out of the structure
Grain and legume together supply complementary protein, the vegetables supply fiber and micronutrients, and the dairy or fermented element supplies fat and further protein.
None of this requires the cook to know any of it. Following the format produces the outcome, which is how the arrangement survived long before anyone described it in these terms.
Portion control is built into the vessels
The small bowls physically limit how much of any one item can be served, and the plate holds a fixed number of them. Quantity is bounded by the equipment.
Rich or fried items therefore occupy the same small bowl as everything else, which caps their share of the meal without anyone deciding to restrict them.
An American plate with no compartments allows any single item to expand into the available space, which is a structural difference rather than a difference in discipline.
Contrast keeps the meal interesting
The roles are chosen so that adjacent items differ in taste and texture: something sour next to something plain, something crisp next to something soft.
That contrast means each mouthful can be composed differently, and the meal does not fatigue the palate the way a single large plate of one thing does.
Adapting the format in a US kitchen
The structure works without any Indian ingredients at all, since it specifies categories. A grain, a bean dish, two vegetables, yogurt and something acidic is a thali in form if not in flavor.
Small bowls or a divided plate are the part that actually does the work. The format's advantages come from the compartments and the category list, not from the cuisine attached to them.