Harmony - Troop Symmetry

This is precisely a "human" skill,

the skills of humans are those used by units of the human race.
The fact that "Guardian Angel" is only available to humans does not mean that they create it. It simply means that someone (angels) creates it for humans.
Magic is magic, and not a skill.
And Special Ability is a racial ability.

we are talking about light magic - the magic of Erathia

not long ago, I suggested assigning a school to a race.
but this is not the case yet...

Besides: the fact that the ability is in the School of Light Magic does not mean that it comes from that school.
For example: the ability of a simple ballista is in "attack"...