He couldve been weakened by all that experimentation done on him and Cloud for the last 5 years. But....if he is a member of SOLDIER doesn't he have Jenova within him anyway? That is after all how one becomes part of SOLDIER. So....why is it that Sephiroth and Lucrecia cling to life due to their Jenova cells but Zack can die without resistance? Plus there's other NPCs who say they were in SOLDIER and I don't really get how they aren't being manipulated like the clones.