Hi Fizzy and welcome to the forum.
Deleting the user content type doesn't sound good. I guess this messed up a lot and will be very hard to fix, if even fixable at all.
So if you are on a fairly new install, I would setup a completely new site from scratch or roll back to a backup before you deleted, if you have one.
Saving of email to user name and user username fields:
This is about storage options. If you open the USER EMAIL FIELD FOR EDITING YOU CAN SEE AT THE BOTTOM WHERE IT SAYS "Storage": Standard - User - email.
This means that the info gets stored in the joomla user table in the field email.
The user name gets stored in the field name and username in field username.
Now when you want to store the email in all three fields, you need to use a plugin
SD Concat. This plugin can get the value that you entered in the email field and save it to other fields.
So you would set up two hidden fields. Both type SD Concat. Name them whatever suits you, but not the same as the standard name and username fields. Leave the 2 standard fields in the form.
Setup your field for user name:
In the SD Concat field settings in "List of fields" you type in "#
user_email#" (without the quotes).
STorage options: Standard->User->name (do
not tick the checkbox "Alter").
Then you repeat the same for the username, in "List of fields" you type in "#
user_email#" again and Storage: Standard->User->username.
When you now create a new user and save it you should see the email address in user name and user username fields.