Courtiers traders and infiltrators have (some) different mechanics and my not appeal to all players. They also have h/p requirements.
For example, infiltrators are literally assassins and saboteurs. You need 40 Honor to become one and will never get h/p while they have this class. If an infiltrator is spotted, they lose h/p, lose enough and the enemy judge doesn't need to ban you to execute you.
Traders need to pay their units more because of the automatic mercenary designation.
Courtiers fill the role of, essentially, politicians. While they do not have access to Diplomat political options, they can improve realm control and use police type soldiers to capture insurrectionists. However, police units perform very bad in combat.
The adventuring skill is only useful (or even used) by adventurers. Nobles can (and usually do) buy and use scrolls from them, as (apart from an IG event while a lord) this is their only way of obtaining them.
Hope this helps.
