I think a distinction should be made between happiness and satisfaction. If one is satisfied with their situation, they will not try to find better possible scenarios or situations. One gets stuck in a rut.

The advantage of the negative viewpoint is the motivation of dissatisfaction; complaining about something will lead to doing it. You're not good enough at writing? You practice. You're not happy with your government? Start a campaign. Etc. This is where the "accuracy" of the negative viewpoint comes into play - it's always likely that there is something that can be improved, in the pursuit of perfection.

However, if it's hard to change, the negative viewpoint is a drawback - for dissatisfaction combined with powerlessness leads to depression. So ideally the two points should be combined. One should be happy with the qualities already achieved, but not content with merely them.