The Unseen were less skilled spellcasters compared to pure elemental mages. However, because of the time spent perfecting their disguises and false roles, they were quite skilled in other areas that elemental mages could not dream of practicing, but were still pure amateurs compared to the true practitioners of their chosen disguise. Examples of these skills included weapons training, stealth skills, etc.
Regardless of the disguise they chose, any Unseen who cast spells while disguised risked instantly revealing their true nature to any onlookers. True practitioners of the Unseen's chosen disguise viewed them as complete amateurs. Those with an attention to detail might be able to discern the Unseen's true identity and react accordingly.