No matter how Vaan thought about it, the development of the Divine Soul Kingdom was imperative. Its utility was multi-layered and essential at every stage, also spanning many areas.
Cultivation, protection, security, convenience, etc.
'Even if I successfully create the grand reversal spell, cheating true death, it doesn't necessarily mean it'll fully restore me to my former state prior to true death.'
His body was forged through various opportunities and inheritances, and even its innate talents were likely given by the heavens or the one who sat above the heavens. As such, recovering all of this would likely require more than just a tremendous amount of energy.
Even if he created a spell capable of reversing true death, to even be able to return from the state of true death was already the greatest blessing. Expecting to recover all his talents, ability, and cultivation would be too hopeful and greedy.
