Offense
As he was thinking about the classes of missions he immediately crossed out covert operations. The skill pre-requisite for the covert operations missions was much more niche and extensive than the other classes. One needed stealth, sensory, infiltration and espionage capabilities that Rui just frankly lacked.
While it was true that Rui had mastered Blink, Blink was not good enough all by itself. Blink had weaknesses, for example, it's timing and usage was largely out of Rui's hands. He could not use Blink whenever he wanted because he needed his opponent to Blink.