What made me insist on this was a discussion on my guild’ chat when someone was confused because another guild pulled a Death from a Legendary Task when Wulf was the exclusive. Up to that point, the person just confused “tasks” with “chests”, and that was their bad, but someone argued:
Just because A is "exclusive to" X, it doesn't mean I can't get B or C from X. It just means that X is the only means of obtaining A.
And they’re absolutely right. And this should be addressed in order to not confuse players. No one wants to confuse players, right? And the fix is not hard at all! You just have to change the wording. Maybe something like
"Only Mythic obtainable from glory, gem, guild and VIP chests."