I believe that answering this question based on the mere complexity of the password generated may miss the mark. While it appears the passwords generated by Safari/OSX Keychain are quite complex and would be virtually impossible to crack with technology available today, this only helps in defeating brute force attacks.
Much more commonly, passwords are discovered through:
- This OSX keychain access should make it harder for malware and certainly keyloggers (since you're not typing anything) to obtain passwords.
- Password re-use
- Reuse of same password on multiple sites means taht if one site is compromised/experiences a breach, hackers will try this username/password combination on other sites.
So, that said, using unique passwords for each site and a password manager like Safari/Keychain increases your security significantly. This security enhancement goes far beyond the simple complexity of passwords, because by using a password manager you're engaging in a best practice that helps defeat numerous types of attacks to get your password.