Praise the Prince

The general consensus on Kaeya Alberich is that he is talented, attractive, and cunning. Also: sarcastic, distant, manipulative. This combination means that Kaeya, despite being regarded overall with admiration, is not often praised. Albedo has no such qualms with Kaeya's duality. So when the alchemist sees Kaeya has done exceptional work, he tells him so.