How likely is a AES KDF bypass?
Let's assume a password consisting of 15 random longish words from several books.  It's likely then that the password's entropy will exceed 256 bits. (This is actually very difficult to compute accurately as there are linguistic /social /physiological issues to human password creation, but let's skip over those).  That's more than that of an AES-256 key.  So in this case it seems that it's worthwhile attacking the AES key directly as it's got less entropy.

This would be a brute force attack directly against an AES-256 key.  The futility of this is well covered on this site.  I'll just add this link and say that you'd need more than all of the batteries on Earth for the energy demand. And a lot of time measured in age of Universe units.  It's impossible and really not worth doing.

It also opens up the question of what would KDFs be for if you simply bypassed them and attacked the cipher key directly?