It is a good idea to try and create a system of resurrection independent of the void universe as it will grant them the ability to resurrect like Origin gods without being Origin gods and they won't lose this ability if the void universe is destroyed. But Legion-7 himself who is to be the foundation of this system is vulnerable.
If he is to try to eliminate Legion-7's weakness then it will take a lot more of his divine ability slots which will disrupt his plan for the other clones. Hence why Legion-5 is not sure they should do it.
Legion-7 made his point. "I don't think we have to think much about it because it will benefit all of Legion and eliminate a very important weakness. After all, if you are unkillable that means I am unkillable. And if I am unkillable then we are all unkillable. If we are all unkillable, then whatever doesn't kill us will only make us stronger."