I still think our KYL writers are way, way too fond of the whole E'lune theory, and more than happy to tear up any bit of established continuity to keep playing with it.

For example, I'll stipulate the idea that diabolical!naaru can control (or at least heavily influence) folks who follow the Light. So in this scenario, An'she pushes Arthas to be extra zealous in his pursuit of first Kel'Thuzad and later Varimathras. Sure.

How does that lead to the destruction of the Sunwell? See, Arthas picked up Frostmourne and consequently gave up his soul to the Lich King; he arguably has less free will at this point than the PC DKs do before Light's Hope. At this point, An'she no longer has anything to control... he's Ner'zul's tool. Which means it wasn't An'she's doing that Arthas later desecrates the Sunwell to resurrect KT, nor is it obvious that that would be something the Lich King would do.

Heck, it's counterproductive, anyway, since as much as the queldorei followed any faith they followed the Light, and this genius 'plan' involves the destruction of two powerful kingdoms full of Light worshippers (Lordaeron and Quel'thalas) as well as dealing the local order of paladins a blow from which they arguably haven't yet recovered.

See, a plan like "M'uru allows himself to be captured to be a beacon of the Light within the sindorei capital" makes sense. It's simple, and despite the hiccups (I somehow don't think the whole "sacrifice M'uru to open a gateway for Kil'jaeden" was sketched into the original plan) it worked, first by allowing the creation of the Blood Knights, and later by transforming the Sunwell.