Ivo had the information but he didn't have a huge force. Rave, on the other hand, had a considerable force but he didn't have the exact information.
So, infiltrating this place before with only their capabilities was close to impossible.
However, that was not the case at the moment. Even though Ivo and Rave were said to be part of the mission, in truth, they were only given the opportunity by Spade to finish what they wanted to do.
As this mission was solely reliant on the military and huge armed forces, a single individual could hardly make a difference on this kind of battlefield.
In this part of the city, the empire army didn't hold back at all, as there were no innocent households around them. However, they did make sure to be careful not to bombard some confirmed places, which could affect the operation and entrances underground.