I see what you’re saying. I think I said this in another comment, but my goal is just to avoid (overly-)sweet foods. From that standpoint, “unsweetened” is ideal. But “no sugar added” for something that’s naturally somewhat sweet (such as tomato paste) is also acceptable. If I were to pick up tomato paste that said “no sugar added” but did have artificial sweeteners, I’d be horrified. So I guess the terminology is more straightforward if you’re avoiding sugar, but it’s less useful if you’re avoiding sweetness.