One big advantage a founder CEO has over appointed ones: the founder CEO can have a thesis about the identity of the company that's used to guide decisions.

An appointed CEO can inherit such a thesis, but can rarely invent one.

Inheriting a thesis is a poor substitute for inventing one, because the thesis of a successful startup usually grows organically out of the founders' personalities and experiences. The appointed CEO is at best wearing someone else's clothes.

Exception: An appointed CEO who had a similar personality and experiences (e.g. from having worked together) to the founding CEO could presumably assimilate the thesis.