Assumptions:
1. People aren't very good at choosing hard-to-guess passwords
2. Complexity (Case, numerics, special characters) don't significantly add to entropy
3. Password managers can create and store high-entropy passwords
4. Password managers must be secured with extremely strong, crack resistant passwords
5. People need to set the passwords for (4). See (1) above
And there's the rub with TFA's assertion that password managers are the band-aid to help us past the era of passwords. If we can educate people to create strong, memorable passwords/passphrases for the password manager, then people can do the same for other passwords. Which makes a password manager redundant.
If we cannot educate people to create strong, memorable passwords, then the likelihood is that password manager passwords will be just as weak as those the TFA is decrying, rendering password managers just one big target.
And since a password manager presumably contains lots of passwords for a variety of logins (including sensitive accounts), it becomes a much better target (especially when you can steal the password DB and perform offline cracking activities) than trying to crack passwords online.
The author of TFA is correct that there are issues with passwords, but his recommendation is poorly thought out and might be even more hazardous than the problem it purports to mitigate.