I've always thought of scarcity and FOMO as different things, at least from a product marketing standpoint.

Scarcity: There isn't much of this thing, so I need to compete to get it. I will prioritize it more highly. There is a scale of desire for this thing. If I believe I need it in the future rather than now, I may defer.

FOMO: 0 or 1. I am going to miss out on this. Is it important to me? If it is, I will prioritize all my resources to get it now. If I believe I need it in the future, I will act now.