Email Address shows login on the final checkout screen:
That is connected with the feature "using e-mail as login". The users created before upgrade to OSA 7.0 can still have logins not set to e-mails.
If you do not intend to use e-mails as logins, set the setting
USE_EMAIL_AS_LOGIN to false:
Home > Products > Online Store > Advanced Settings and synchronize the store.
If you intend to use e-mails as logins, plan to enable CCPv2, then after CCP v2 enabling all the customers will be asked to change the login to e-mail address.
Otherwise you can modify
confirm_part4 layout template as required (do not forget to set some description for the customization, so that you do not forget the reason why it was done).