With Jack's incorporeal state, it didn't take long for the four to go down the labyrinth. The monsters of the first half of the floors were nothing to them. Their challenge was simply to find a way through the maze. Since Jack's incorporeal state eliminated that challenge, it became a walk in the park for them.
In a short two hours, they were already on the tenth floor. The monsters on that floor had levels from 45 to 50.
The drop rate was still terrible, but the mana core drops from the bosses were decent.