Originally Posted by
therealbowser
A more accurate way to look at it is like a triangle. Arcane power is weak to fel, so Sargeras was able to defeat the Pantheon with fel power. But we don't know what the void is strong against... I'd assume that the void is weak to the light, but who knows if that is even true.
My headcanon for magic in WoW is probably this:
In terms of sheer, unbridled power (with all of the advantages and disadvantages), fel is surely the most powerful and destructive, but has little control over its power and exists almost entirely as corruption of other magic schools rather than a natural style of magic.
Void is probably the most corrupting (and devouring, by nature it consumes all it touches and is never quenched).
Death magic is the most overwhelming in how it saps life force.
Arcane is likely the most balanced force of power; it is supremely powerful, but limited in some ways, and easily corrupted. As it is the magical school most strongly connected to order, it depends upon being utilized correctly. It may exist as a combination of other various types of magic, even.
I cannot speak for natural magic (frost, fire, nature, etc), but it is by far the most versatile and variable school of magic, and it takes many forms and melds well with arcane power (which may explain why mages who utilize arcane magic heavily also have schools for frost and fire, and why druidic magic which is primarily nature-based utilizes arcane-based lunar magic so well).
Lastly, holy magic, while it lacks the sheer power of other schools of magic, is by far the most resistant to corruption (in the sense of being corrupted to a different type of magic) and the most piercing... which is why it would be effective against void, fel, and especially death where other magical schools would be ineffective despite being more powerful.
But, this is again, just my headcanon. Blizzard as far as I can tell has not elaborated upon this directly, but in short, as far as we can tell, void is just the next big bad we are dealing with. It's the void lords that are powerful (perhaps because they consumed so much power to become what they are?), rather than void magic in and of itself.