Originally summons didn’t exist as troops you could get, but eventually the devs switched it so all summons had a card and any time that unit is summoned it mimics whatever you have that card at.
Assuming this is the case, it probably is taking whatever the enemy has their wraith at.
Nope, mine is level 19. And my Spooky Imp is level 19 as well.
So, I imagine, the original intention from the devs really was for the summoned Wraith to be level 12 (which is awesome btw). A pity it’s not working properly.