gotta use what you have....
it's why i have a whaleship that's still below 800k power (without the help of a friend) and i have to farm magic based missions for now.
which kinda makes it interesting cause weakness abuse makes up for about 30%-50% of the power you should have to reliably clear the stage, hence why stages that want around 1.1 mil power are still doable for me if they're magic-weak enemies
If I get a duplicate character from a summon, it's typically going to be used to level-up or otherwise improve the character it's a duplicate of, or another character that's lagging behind a bit on levels. New characters, I can either take or leave.