The formation of the army could not be delayed, but Saleen could not stay behind either. He had to go to Holy Rock City. Saleen had already made a promise to Joey, and now that he had hopes of becoming a sorcerer, he would be in hot water if he still did not go.
Everything there had to be left to Lex. The defense of Metatrin City would be left to Jola while the formation of a new army would be left to Daniel. This sort of delegation was related to Daniel's profession too. In the event that a war erupted a death mage would have an endless supply of resources. Deploying Daniel onto the battlefield would not affect his training.
Daniel was born in the Tanggulasi Empire, he would not be attached to Qin. He would not have any psychological barriers when attacking Phoenix either. Even if Daniel was sent to invade the Tanggulasi Empire, would be very exhilarated, Qin would be no problem.