The reason her sin was so bad is because of what it lead to. Think long term with Eve's sin. Because of what Eve did, almost 1000 years later not only one country but all of Evillious could be destroyed by Nemesis. Irina's actions lead to the end of Levianta but in the eyes of the people of Evillious they don't even know who Irina Clockworker is. Eve is someone they all know though as the one who brought the Seven Deadly Sins into the world.