This isn't specifically a "Legends" board as far as I'm aware. It's an EU Board. That can include Official Canon EU as well like TCW, Rebels, and the new Tarkin novel.
But your right that it's not a good idea to start mixing and matching Legends continuity with "the new" Official canon continuity. Because they don't recognize each other, so don't mesh.
On the other hand every time we used to discuss feats from the movies in the EU section, we basically were mixing and matching EU with Official canon. But I suppose that's because The films were canon to the old Legends, whilst Rebels is the start of a new Canon not apart of Legends continuity.
Yeah, S-canon and below all existed within the same continuity, whereas Legends is basically about as canon now as those Infinity comics were to the old EU- i.e. it's more or less a bunch of "what-ifs" or alternative histories.
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"The Daemon lied with every breath. It could not help itself but to deceive and dismay, to riddle and ruin. The more we conversed, the closer I drew to one singularly ineluctable fact: I would gain no wisdom here."
She didn't lose to him. She battered him badly. He was on the floor at her mercy but she refused to strike him down and committed suicide.
But whole fight was circumstantial. It began with Mace having lightsaber hole in his gut. She was getting stronger from fear and death of soldiers around and Mace was refusing to use Vaapad.