Both dramas are directed by the same director and are short suspense dramas. The story also focuses on a trio but in The Long Season there are two trios that span two generations.
Both are suspenseful historical conspiracy dramas surprise twists, have hidden/multiple concealed identities, betrayals and use art of war like strategies to trap and defeat the enemy.
They are both conspiracy heavy historical suspense dramas. They also have a revenge theme. Both are set during the Ming Dynasty. Pledge of Allegiance takes place in early Ming and The Ingenious One in mid/late Ming.
The title says it all. It also has two male leads although only one is the detective and the other is the muscle.
Another ancient investigative team led by two male detectives and a eunuch. The eunuch is a grey character very much like one of the two leads.
The Imperial Coroner is another ancient investigative team. It is more of an ensemble cast but the way the cases are solved are procedurals, which is similar to League of Nobleman.
They are both ancient detective dramas where a team led by two lead detectives investigate mysterious cases.