I'm not really convinced about the never having online backups. If you encrypt them with a strong enough password, then it should be pretty safe.
If you think about it, every Bitcoin address has a unique "password" and is "stored online". If you have a strong password for your keys then it would be as safe as anyone trying to guess your key anyway.
Of course, unencrypted keys, or keys encrypted with a weak password would be easily compromised if found online.
But, you know, the problem is that most people use weak passwords.
A proper password must provide security of 100-bits or higher, while also avoiding dictionary attacks.
Examples:100 bits of entropy, avoiding dictionary attacks: k9OS_j1Bnmp!5sPr
100 bits of entropy, susceptible to dictionary attacks: 1Bankruptcies2&%
[1]Apart from that, if your password is as complex as it should be, then you need to write it down and store it safely, in more than one backups.
So you just transpose the whole backup efforts from your seed phrase to your password / passphrase. I don't think it's worth it.
[1] source:
https://proton.me/blog/what-is-password-entropy