I never said to use Gul'dan again. The Legion could have employed a different agent.
The Legion did not invade Draenor to wipe out the orcs. The Legion was there with the intention to kill the draenei. Remember: Kil'jaeden was on a personal crusade to erradicate Velen and his draenei.and invasion just to wipe the orcs is not worth the effort since draenor is useless despite some cannon folder potencial