>Your argument that "any adversary can read the vault from memory" is a weak one, we might as well not have passwords with that attitude.
It all comes down to threat model. If you don't have malware on your machine, 2FA and passwords are quite useful. If you do have malware on your machine, they're basically useless. This is basically the same for any service. Name one website or program that's safe even if you have malware on your machine.
>If one of those factors is stripped away for "convenience" we're misunderstanding the point of 2FA entirely. I can't make this any clearer.
It's not for convenience. It's because there's no practical way to implement encryption/decryption with 2FA. You seem to think there's some practical way to do it, but there isn't.
Lastpass 2FA protects against the threat model of an attacker who has stolen your password. In that case, the attacker cannot steal the contents of your database because the attacker can't get any form of the database, encrypted or decrypted due to not having the 2FA. Unfortunately now that an attacker has stolen all the encrypted databases by compromising Lastpass itself, this threat model is no longer realistic against this one specific attacker or any attackers that this attacker shares the loot with, because they now all have your encrypted database.