Why is P2PKH used instead of the simpler P2PK? If elliptic curve cryptography is secure enough to be able to give away a public key without fear of anyone being able to calculate our private key from it, what's the reason for hashing our public key for use in P2PKH?

In other words, what's the benefit of a more complex system for locking and unlocking bitcoins, if a simple P2PK transaction is secure enough?

I'm not against extra security, but why is it not considered to be redundant?
The original reason why addresses were a public key hashes is something you'll need to ask Satoshi. My guess however is that it was just shorter and more convenient (note that compressed public keys weren't known at the time).

When compressed public keys were discovered it was simply easier to stick to the existing address scheme (it didn't require any changes at all; wallet and node software happened to already support compressed public keys). Introducing a new address scheme that was both more expensive for the sender (34 bytes of output script rather than 25) would have been nearly impossible to convince the ecosystem of - knowing that deployment of P2SH even took several years.

One often repeated argument in favor is quantum resistance. I believe this is besides the point. We have no idea what the characteristics of a hypothetical machine relying on yet to be invented technology will be. Given the degree of key reuse on the network (so there are addresses with known public keys), the existence of a system that can break ECDSA is likely a death blow to Bitcoin. A real solution to that is to prepare and have real quantum-resistant cryptography in place before it's too late. Relying on a weird hope that those hypothetical machines are somehow too slow to steal from unconfirmed transactions before they're mined is a red herring.