What will account abstraction achieve that smart contract wallets absolutely can't do?

If we create a smart contract wallet which

1. Takes a custom signature as an argument in every function
2. Verifies the correctness of the signature before executing any of the function code (a modifier basically)

And the signature can be anything, a SHA256 signature, a google sign-in verification method or whatever the user desires. So basically, any address can call the contract as long as it has a valid signature. Then technically, haven't we managed to

1. Implement custom signature schemes
2. Eliminated the need for a seed phrase because any address can call the smart contract. The user just needs to know how to generate the signature
3. Implement any possible code in the user account (the smart contract) like auto debit, 2FA etc.

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So my argument is, while a lot of people are waiting for account abstraction to become mainstream if it really was that game-changing, why isn't everyone switching to smart contract wallets today? Or what am I missing here?