With a PoW blockchain you do not need to trust the genesis block. You can calculate the total amount of work represented by any blockchain which provides an independent measure of trust. Total proof of work can be calculated with just a copy of the blockchain data without trusting the software client. Nothing like that exists with proof-of-stake.

If the assumption is that downloaded binaries must be trusted, one could simply use a key embedded inside that binary to verify the identity of a centralized database. No need for proof-of-stake.