I figured this out when I restored an iPhone once. I was also told I needed keychain for HomeKit, but all is fine.So, your point about the 1Password weakness has been raised on the 1Password forums. A member of their security team did respond. Basically they said "Trust Apple".
https://1password.community/discussion/comment/590911#Comment_590911
Yeah, that's something that 1Password post did suggest. I've decide to leave mine on, but only because I do have a number of carefully secured devices that are consulted whenever unrecognized access to my iCloud account is attempted.
Good point. The forum post made that point "If an attacker managed to breach iCloud and acquire your Secret Key, they would still need a copy of your encrypted data itself, as well as your Master Password in order to decrypt it."
But, 1Password is no longer as rock solid as I thought, unless I turn off iCloud keychain.
Now with iCloud, a person would need your Apple ID password, the Apple 2FA, your master password for 1password and then 2FA again (if you have it set up for 1Password). So, it would be a lot to go though to get to your passwords on 1Password.