I'm assuming the ritual you're referring to is the one in Prophet's Lesson? If so, from the description it seems to be less due to inherent magic of the world or the warlock themselves, and more due to the runes and symbols themselves (i.e.: something like words of power that themselves have magic). Although, I don't think it's ever really been explained, though I think the idea of some symbols having inherent power (and if you used them carelessly, that power could backfire) would add some texture to the setting.
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Regarding the ability to destroy worlds, there are many individuals who can do so. You have the Titans (as a given), the Void Lords (Pandemonius destroyed the Ethereal Homeworld), cosmic elementals (as demonstrated by Murmur), high ranking demons (Archimonde, and presumably Kil'jaeden), and the Aspects (Deathwing and Malygos both had the power to create these conditions because of their Aspect). It's also likely that any cosmic counterparts to forces that can manage these feats, such as the "Light Lords" or any possible "Chaos Lords", would be able to do so as well. Then, as you say, we have a large number of rituals that can have the same effect, including lesser known ones like the Darkstorm made by Xaraax (who, as an aside, was a Dreadlord who was planning on destroying Azeroth, which I guess was just another one of Zovaal's 5th dimensional chess moves), and we know that demonic portals frequently have an unfortunate side-effect of imploding (as seen by Illidan's destroying of Nathreza), which would probably imply that Legion generals like Portal Keeper Hasabel could also pull off something similar. Finally, you have the fact that many magical implements and facilities are known to have the same effect, such as the Forge of Souls, that was capable of killing Azeroth and is what Zovaal relied on, and the Forge of Origination, which could re-originate the planet (and I think reasonably it could be extrapolated that redirecting this power could likely also kill Azeroth).