Of course you can, just adjust the recipe to your own taste. Garlic has a strong, savory flavor that can help to balance out the acidity of tomatoes. When garlic is added to tomato soup, it helps to create a more complex and well-rounded flavor. The garlic also helps to add depth and richness to the soup. Roasting the garlic with the tomatoes helps mellow down the smell and the flavor a bit. If you were to saute the garlic with the onion, then I would use only 3-4 cloves, but because I'm roasting everything ahead of time then I can use a lot more.