Chaos bolt and fel flame weren't, they were the things that made the contrast to the otherwise red themed destro warlock. Now with green fire, where is the contrast for that? Well it's not the mount anymore apparently.
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Demo is less of a problem as they had soul fire, hell/immo aura and mount as a contrast, however with green fire not only the fire is affected, but meta form, leap, DA etc things that were previously purple got changed too, along with the mount, which just overall makes green too dominating.