Then please, tell me how it exactly works to give me more security to log in with my display-name. Maybe I'm not smart enough, how will that work to give me a better protection?
Display-name has been done for F2P as I assume they don't need Origin. It was a need.
Now, not allowing to use e-mail don't improve the security for your account, but do not decrease it either. However, by not filling the ID entry with your e-mail, it makes it more complicated to "steal" it. Then your e-mail is less in danger. Same goes for your Origin account.