Technically a "wallet" file contains your keys (public or public and private), addresses, transaction history and unspent transaction outputs (aka coins).
Your seed phrase is the "master" key that would create all your keys, this is why the only thing you need to backup is that phrase and you can recover it using any wallet software that supports the algorithm; but you still have to create a wallet to get all your keys and transactions and sync to be able to know your balance and spend.

Technically what we discuss here is jut a key derivation function and KDFs existed before bitcoin and blockchain technology.
This technology is revolutionary for many reasons such as being able to create decentralized money.