Except there's no retcon whatsoever here. The leader of the Council of Six never had such an authority. Anthonidas didn't arrest Kel'thuzad alone either, and that's much smaller action against people of Dalaran than what Jaina did. And as Tides of War showed even before Jaina became the leader, they didn't get a tie-breaker vote.
Please, Metzen confirmed years ago that it's the same Alliance. Arthas had no authority over the Alliance to dismantle anything. As for the starting Blood Elven questline, when you are in diplomatic talks with someone and use them as an opportunity to sabotage them and invade their land, you most certainly did betray them, because diplomatic talks carry certain obligations of behavior.
Could you, I dunno, read the entire posts? Because I already said what Teldrassil was 2 paragraphs earlier... This forum makes me really sad at times.