Although you seem to have concluded your opinion in way no longer open to refinement, I think I've made a compelling case that the heroes' victory over the Legion was neither easy, and that the Legion were presented as a legitimate threat in all three phases of the story-arc.
That link doesn't work.
I actually liked Kil'jaeden's brief foray into sympathetic acceptance of his fate following his defeat. He didn't cower from what he felt had to be done, he only decided to do it on his terms in the time he had left. Recognizing his own folly when it was far too late for him to do anything about it concluded his story with a degree of poignancy. I agree that some kind of redemption arc for him wouldn't have gone over so well - but fortunately that didn't happen.
Technically we only conclusively imprisoned Sargeras and (probably) Archimonde and Kil'jaeden. Argus was never proven a place where demonic essences were dispersed on death - and since the named demons we killed were either before that or while Antorus was functional and active it's possible the bulk of them are still regenerating in the Nether. The head of the beast has been removed, but its many coils may still remain to bedevil the heroes in other settings.
That's an interesting parallel you keep bringing up, and you still haven't explained how you see the Scourge as having victories in some regards while you simultaneously deny the Legion victory in any context. The Scourge succeeded in taking Lordaeron in WC3 and that's a Scourge victory, but the Legion taking Suramar isn't a victory for the Legion? The Scourge are defeated along with the Legion in the Third War, pushed back to lick their wounds at Icecrown. The Legion take Suramar but are eventually cast out by the Champion and the Nightfallen Insurgents (in conjunction with Night and Blood Elven help). It seems very unfair not to extend the Legion the same courtesies that seem so easily granted to the Scourge, especially considering that *both* forces have been conclusively defeated by the heroes of Azeroth.
I don't know if you've run through the Antorus raid, but it definitely is very high up there with one of the most epic experiences WoW has yet to offer. In the opening wings of the instance you can see far-off battles happening with Army of Light auxiliaries and Legion forces going on, giving the instance an organic feel like a living and breathing battlefield. That's not something I've seen before in a raid - that feeling as if you're part of a veritable army storming the gates of an imposing fortress. Flying the Vindicaar from wing to wing to take out objectives, and encountering a number of tableau were others are just as in the thick of it as you are.
You had to rely on an external "omniscient" standpoint to prove your point, while I was talking about the outcome from the internal standpoint as the characters would be aware of it. I don't think Azeroth is going to do die in BfA either, but my character can't know that and so to them and most of the other characters living within the story the wounding of Azeroth is a very serious thing. It's a victory won at a ruinous cost - which is pretty much what a Pyrrhic victory *is*.