The drop rate for the potential artifacts in that particular mission is horrendously low, maybe the lowest of any mission in the first twelve chapters. (YMMV)
I play all Wendy's shop and the theatre vids every morning to back up my choices for gems/gold. If I'm charging my mobile I'll go for a second run when I'm home.
To get items for the triune...unless you need stones for other heroes. It is a way to get the daily done if you are building heroes that you do not have to do heroic missions.
