"Oh, there is so much Dukkha." We have to also remember the true cause of it and the way out of it, the Four Noble Truths. Contemplating the Four Noble Truths is very helpful, but this question is asking about the Brahma Viharas. So, yes, Sympathetic Joy is very helpful for remembering the way out. It's also helpful to remember Equanimity. "Oh, so much Dukkha" - it sounds like there is a little bit of self-pity there if the person is just thinking about their own Dukkha, so it's helpful to remember Compassion/Lovingkindness, especially the D/D method, so that we see that our Dukkha isn't so much; we put it into perspective. If the person is reflecting about all the Dukkha in the world, then, yes, Equanimity is helpful to understand what we can and cannot control, to understand that this is the nature of existence and it's not within our power to change the nature of existence. We can only transcend existence from what I understand. That is, transcend the wish to be born.
Lovingkindness. If we're focusing too much on Lovingkindness, we may be getting rather happy, just thinking about the happiness of people and getting overconfident, feeling that it is easy to love all people, all beings. It shows that we do not have enough Compassion to strengthen that Lovingkindness. If we feel that it's easy to love all beings, we're normally in for a fall when the warm feeling we are used to getting goes away when we are confronted with difficult people.
Sympathetic Joy. With thoughts of Sympathetic Joy, we may be getting high just thinking about the good qualities of ourselves and others and forgetting about the Dukkha in the world. We don't want to forget the Dukkha of others. If we're actually getting giddy and only thinking of the good qualities of others, it leads us in for a fall. We need to have Compassion and Equanimity strengthening Sympathetic Joy because we need a balanced view, not only of ourselves but also of others so that we understand Dukkha does also exist.
Equanimity. If Equanimity is unbalanced, we're not caring much: "Oh, that's their problem. I'm not going to take any notice of it. It's their problem; it's their responsibility." Perhaps we need to strengthen and balance our Equanimity with Compassion. Or we might have thoughts of, "Well, don't they know everything is impermanent?" Well, yes, everything is impermanent, but sometimes it's very difficult to accept it for human beings. If we get into judging people from our understanding and our wisdom, then it may be that we don't have enough Compassion that precedes our Equanimity. That is, we have to learn how to care first before we go into the Equanimity. We have to make sure we care. Otherwise, our Equanimity can be a mask for aversion and indifference.
So, yes, the Brahma Viharas need to be balanced. These are some of the thoughts that can arise that gives us a clue if we are off-balance. Having a lot of the judgmental mind gives us a clue that our Compassion is perhaps lacking. We also may not have Equanimity at that time since we may be thinking we can control ourselves and others.