I'm in my prime.
I believe the "you" in leader text means "the player", not "the leader". So yes, the player who chose Karin as leader doesn't use up an action to attack; this could mean a vanguard wave in which you attack with all three front-line heroes and then draw two cards (or whatever).
Thanks! I also thought that the "you" is the player. So that means that in each of the three waves, I can make as many legal melee attacks as possible?
Appreciate the response.