This trait has been annoying us since forever with its pointlessness. If someone wants to waste a team slot on a second Great Maw on the chance that enemy team has two troops that are not immune to devour and won’t just autowin when(no, it has never been “if”) AI gets a zillion extra turns from the gems the Maw generates then let them.
All of these troops except Sky Scorpion have too high mana cost to be able to cast in a quick match and any match that lasts longer will have AI troops that will either win before you collect enough mana or too high stats to care that you have a second Roc or Archdeva in your team.
Dwarven Slayer having it doesn’t even make sense, the troop already dies while doing far less damage than its mana cost is ever worth so having extras is the only way that troop can ever be useful.
Only useful reason for this trait to exist is so annoying people can’t set four Daemon Gnomes as defense. Without it some of these nine troops might occasionally be put on a team.