My own impression from a week in Paris is that you're right: if you get the "menu" at most restaurants (appetizer, entree, dessert), you walk out full but not stuffed.
The weight-loss drugs like Ozempic, supposedly make you feel like that. I haven't taken them myself. It's like you don't really want any more.
Americans seem to feel entitled to two meals for the price of one, and they may or may not eat them both in the restaurant. (If they don't finish, they take the rest home with them)