Daekol's setup was not complete. More than preparing to face the human Lex, his preparations focused on the Dao Lord backing Lex. The prep involved hiding their location from tracking so that once he made his move, and the specific Dao Lord detected something amiss, they wouldn't be able to find Lex and Daekol.
Moreover, he had to make sure that there was no interference from the Dream realm, which was expensive but not impossible. The area needed to be kept safe until his operation was complete, which may be short or long. He also needed to be sure that Lex wouldn't be able to escape using the Midnight Inn's famous teleportation abilities.
Thus, it was obvious that there were many things that needed sufficient preparation. Fighting, subduing and then subsequently defeating the human were actually the least of Daekol's worries.
