This is not inconsistent with one of the fan-theories I touched on yesterday!
I hesitate to speak definitively, but I do see circumstantial evidence that suggests UU could be a Sylph class.
Also, in regards to Kanaya, the assignment of Sylph to her could be as much a class “challenge” as a class “fit”. After all, Virgo is an earth sign within traditional Greek-influenced western mysticism, and is often associated with the sensual aspects of both life and death (playing perfectly into Kanaya’s role as an attendant to the “mother grub”). And on top of that earth is often given the feminine aspect, and has traditionally been represented by female deific figures rather than male (Demeter, Persephone, Proserpina, Ceres, the Horae (goddesses of the seasons). Hades is the only notable exception from Classical mythology, but even he occupies an exceptional role - he is not a god of earth, but of the underworld, the sovereign of a realm closely tied to the earth, but separate from it).
In short, Kanaya’s element is earth.
*(especially entertaining considering that she is a Hero of Space. On a semi-related note, Jade is also a Hero of Space and her name is drawn from the name of a rock with a rich green hue. Clever girl!)
However, while the mythical representation of sylphs is sparse, they are consistently described as “airy spirits”, so it’s easy to assume that the Sylph class’ element is air.
Kanaya’s assignment of an “air” class, even though she is an “earth” player, was probably a challenge imposed on her by SGRUB in order to help her grow so that she could (theoretically) realize her full potential at the god tiers (had things not gone catastrophically wrong, that is).
It could also help explain how smoothly Kanaya transitioned from the stolid, dependable counselor to her companions that she embodied at the beginning of Act 5, to the chainsaw-happy wwizard killer and clown hunter she has more recently become, since earth’s primary and secondary alchemical traits are “cool” and “dry”, while air’s are “hot” and “wet”.