You shouldn’t use iCloud Keychain for all your passwords (timefrancesco.medium.com)

Bad article. Its only argument is "iPhones are secured by 6 digit PINs, while a "real" password manager is secured by a strong password".

Guess what? My iPhone is secured by a strong password, and the swaths of people introduced to password management by iCloud keychain wouldn't otherwise use another password manager or a strong password.

TL;DR The iCloud Keychain secured by 6 digit PINs which has high possibility you have shared with someone else, thus you shouldn't use it.