umm, no. I have 1024 bit keys and they have continued to work fine from my Mac to various servers that have the corresponding public key. (yes they should be updated, but I have larger keys for other servers).

I use the stock ssh in /usr/bin/ssh

Perhaps you had dsa keys? Those were deprecated and support for them was dropped.

> You can leave this blank or add a password for a little extra security (and a lot more typing).

Please please stop saying things like this. If typing the password is inconvenient to you, store it in your keychain. OS X/macOS makes this trivially easy. Having a pass phrase on your private key is (almost) as important as using a key with sufficient entropy.

Never heard of ssh-copy-id? Copy & paste public ssh keys is a kindergarden solution.