>>715415120>the Great Khans are also the decedents of Vault Dwellers, being from a Vault only goes so far.Well, yes, being from a vault does not guarantee that you develop a functional society. Some former Vault populations devolved. Some self-destructed (see Vault City).
But it is a fact that being Vault gives you an insane head-start and the tools to succeed. It's just that not every one will make use of that advantage.
The more extreme cases of fucking with the vault inhabitants aside (god I actually genuinely hate the whole "vaults were just social experiments" plotline), Vaults store data, materials, tools, and training regiments that actually give you the option to start rebuilding society. Even without geck. An advanced society needs not just knowledge, but also infrastructure and practice. But the thing is: vaults actually provide/maintain all three.