If ever there was a card to be Errata'd, this would definitely qualify. You're spending 4 resources to effectively deal 12 damage. Sure, it's restricted to the boss - but that's your win-condition, so not really that big of a deal. That's a 3:1 damage ratio on a Basic ally card that literally every Hero can afford except an early game Iron Man. If you're playing a Guardian Hero, it's hard to pass this card up just because of its hyper-efficiency.
Also worth noting; this essentially makes a card like First Aid a 2 resource 6 damage attack.