
Personally I don’t see it as a cowardly act because if you think about it, Howard is the one who went after Iris first who was as defenseless as someone tied up because she didn’t possess any strength to fight him back, so the five are just giving him a taste of his own medicine. Howard is already known as someone who just raises his hands to people who are weaker than him so it’s obvious he’s not someone to fight fair or “Mano a Mano”, so it’s a good thing that the five got to let him experience something that he inflicts upon others, being defenseless at the hands of people who are stronger than you.
Personally I think it's pathetic and cowardly just to beat up somebody who's all tied up. If he was untied and fighting him mano a mano that's one thing, but at this point, Ian is just lowering himself to Howard's standard.