You still need a passphrase to decrypt the private key. If you bump up the number of trials, you can make decryption even slower. It's going to be harder for someone to crack that than a normal brute force against a password.

Now, if you put that key behind a decently secure storage service that you use TFA to access, that's actually way more secure than just using a password.

Given that, the question ought to be whether you upload the private key to the cloud, or try to manage the private key yourself. Password based authentication shouldn't be one of the options you are considering.