Is happiness not a form of approval? The experience of approving of the present situation? Not necessarily of a political situation, granted, but given that factions in Stellaris progress – based on support – from nothing to riots and open revolt isn't happiness a better thing to track? Disapproving happy people might join movements but they tend not to turn to violent resistance.
I'm not convinced approval isn't also an emotion anyway, or at least inseparable from emotion. The central problem of trying to represent anything emotionless is we don't know what that encompasses, what something intelligent but without emotion would be missing, or even if it is possible to be complexly intelligent and have no emotion.