The starter city's barrier was supposed to vanish in a few hours after the four factions' meeting. Tang Shaoyang himself was waiting for the barrier to disappear as he wanted to find out what he could get from the eleventh floor. That was right; he was trying to explore the eleventh floor by himself.
After the meeting, the Tang Empire decided to send only the Intelligence Division only to explore the eleventh floor. They wanted to avoid a fight. Hence the Intelligence Division was the best division to send out to explore. With their stealth ability, it should not be hard to avoid the other faction's eyes.