Is that drop rate really so low on a beginner mission?

I have most of the campaign on normal at three stars. I tried running these mission with 4 members as training to while trying to do these challenges and got nothing. Then someone told me in chat that i need to 3 star it to get a higher chance of a drop. So I ran it with 2 champions and it did not help.

What am I doing wrong?

Is there anyway to skip these missions or get more energy? I am kind of stuck.