A few comments,

1. make sure your ~/.ssh/authorized_keys file is chmod 600.
2. the identity file for ssh (-i) has always been the private key, not the public key file, perhaps the old client would quietly accept the public key file
3. ssh-copy-id is a handy utility for putting public keys in place on your servers
4. you shouldn’t normally ever have to ssh to root, ssh as user and sudo is the secure way to do this
5. Use IdentityFile option in .ssh/config to permanently setup the use of ~/.ssh/id_rsa