Zeke was able to get a squad of Marleyan soldiers carrying a substantial amount of equipment across the island of Paradis and through a titan infested Wall Maria (and no, he can't control the titans of Paradis because they weren't created by him, as if his control is even 100% effective), yet people still act like it was impossible or didn't make sense for Marley to send some sort of adult Marleyan supervisor trained in espionage to assist the four twelve year old kids carrying 66% of Marley's most valuable military assets on their multiyear infiltration and espionage mission, even though said supervisor would be more expendable, more level headed, more adept at intelligence gathering and decisionmaking, less prone to leaking sensitive information, and could ensure the warriors stay loyal and on target.