What's the purpose of dupes in this? I had a double Foxy draw before, which I discarded. But I have to wonder.
You need dupes to upgrade their skill rank which is extremely important because at +3/+6/+9 it either adds new effects to skills or unlocks entire new ones that have a massive impact.
Skill levels are ultimately essential later on for most (especially lower than 5*) units to be viable.
That's why skill books are so highly valuable - they replace dupes.