When the sauce reduces down in the cooking process, the sweetness of that tablespoon of sugar is going to be more pronounced, especially with the sugars from the onion, tomato, and tomato paste adding to it. Sugar in a tomato sauce should be added to balance it out when there's too much acidity, which varies depending on the tomatoes. Adding it as a base ingredient to the sauce prior to tasting it is going to be inconsistent.
I'd say nix the tomato paste and sugar from the recipe anyway. Guess we all do it a little differently, huh?
Salt pork, onion, garlic, thyme, beef broth, tomato puree, crushed San Marzano tomatoes, bay leaf, salt. That's all that goes into mine.