Suncrest is the focus kingdom for the campaign in which the mythic and the weapon belongs, and that means similar to the previous campaigns that Suncrest is the final week of the campaign.
I’ll qualify this statement with the “not a dev” disclaimer, but I can probably say with 99% confidence that this is an intentional design choice. The devs are not going to allow players who did not obtain this weapon in the Elite pass for the campaign to obtain it so easily or soon after the campaign ends.
