The second ray carries a structural claim that none of the others do. Bailey's Treatise on the Seven Rays holds that the entire solar system is itself a second ray system, so that love and wisdom are not one option among seven but the key the other six are played in. Every ray, on this reading, is eventually expressed through the second, and a soul on any ray is working toward a second ray outcome by a different road.
That claim does a lot of quiet work. It makes the scheme monist rather than merely descriptive: the seven are not equal alternatives but a single purpose refracted, and the refraction is temporary. It also explains why second ray language dominates the derived literature. Teaching, healing, patience and the drawing of things into unity are the terms in which the whole system describes success, whatever ray it is describing.
Read critically, the claim is unfalsifiable and was never offered as anything else. It is a metaphysical premise, stated as one, and the scholarly study of Western esotericism treats it as a nineteenth and twentieth century construction rather than a report of anything older. Read sympathetically, it is the reason the ray scheme has been usable pastorally where other typologies are only descriptive: it gives every type somewhere to be going. The second ray is where the system says the destination is, and the atlas records that as a claim of the system rather than as a fact about the world.