Within the Demon Peninsula, there is no holy power of any kind; any trace of the Dragons' power is completely erased by the barrier. Ragridia, the Dragon King who rose up against Magus, was completely destroyed; any prayers made to him are meanigless. Holy magic hasn't worked at all under the barrier for a thousand years, and humans have forgotten the art. Instead, human mages and clerics adapted shamanistic (elemental) magic for healing, and call this "White Magic".
"Black Magic" can be divided into two distinct categories: destructive shamanistic magic, and "real" Black Magic, drawing power from a Mazoku. Shamanistic magic is directly controlling the elements and manipulating natural laws. However, calling out power from a Mazoku reuires speaking a contract, and the Mazoku from whom the power comes from must be alive (when Gaav is destroyed, Gaav Flare stops working). Mazoku magic is vastly more powerful then shamanistic magic, but also much more difficult. Also, mazoku magic is strictly destructive n nature.
Eldar races like dragons and elves can use extremely complex and potent spells no human could replicate, but they also can't or won't call on the power of mazoku. Only humans will do this.