This bugs me as the name is more befitting to a chaos lore spell. Is it intentional or does "U'Zhul" mean something else for Bright Wizards?
Not to put too fine a point on it, magic = chaos. There are too many quotes to try and list them here, but I like 2e's The Nature of Magic (pg 140):
As Magisters see it, to use magic is to give shape to the stuff of raw Chaos. A Wizard uses his will and his very flesh to form a conduit between this world and the immaterial realm (known as the Aethyr and the Realm of Chaos), drawing power from the “winds” of magic.
So your statement that the name befits a chaos spell is right on the money. All arcane spells are chaos spells, including all of the Bright Lore spells.
One possibility: it is nothing more than "lore," hence the "legendary." In 2e, as noted the Realms of Sorcery and elsewhere, the Bright Wizards are the first and oldest College of Magic, with a lean toward warfare.
The Khorne/Khaine aspect may be part of the lore of the College as taught to humans by Teclis and the lore masters in the Great War in the time of Magnus the Pious.