This is exactly what DKIM means, and this is why it has wide adoption, while S/MIME and PGP-signed mail remain relegated to niche uses.

The entire purpose of DKIM is not to prove that the individual behind john.smith@gmail.com sent the message, but that a legitimate server owned and operated by the entity behind gmail.com sent the message. It's mostly there to reduce spam and phishing, not to ensure end-to-end communication integrity.

This has nothing to do with the particular companies involved nor their particular trustworthiness.