Your intuition is correct, modifiers like sugar or creme will only obscure a lot of nuance so connoisseurs, professionals & judges will try new coffees or espresso as brewed without adding anything.
Depending on the quality of coffee and a person's preferences they may sometimes add something after the initial taste. And some connoisseurs may order something like an espresso macchiato (espresso with a tiny amount of textured milk) or routinely add e.g. one sugar when drinking a coffee that they are familiar with or just for variety. But in general the better the quality of coffee and the more serious the connoisseur, the less likely they are to be adding anything to their coffee.
Certainly if you are trying to discern what a new coffee tastes like, you shouldn't be adding anything initially (coffee roasters and buyers have a special method for tasting nuances in new coffees called cupping). Even if you customarily like to add something if you want to learn more about coffee and improve your palate you should at least have a sip before adding anything so that you develop a better ability to discern subtle differences.
Espresso like scotch can be an acquired taste for some and they may find that they add less sweetener over time as the intense taste grows on them. And it's worth noting that high quality coffee has a rich, winey base overlaid with desirable flavours and little, if any bitterness. And properly textured milk in lattes is already quite sweet and creamy in texture so there is little, if any need for additional sweetness.