Login with Username vs. email

Dear support team,

on my site, I also have a forum incl. user profiles, and thus also use another login widget.
I found that pretty much all login widgets – be it 3rd part or those of the forum plugins – use the username and password to login.

GD uses the email.

That creates confusion, since users that registered via GD, but then try to login via another login widget don’t know what to enter in the user name field (… or in my case even get lockes out after some tries with their full name.)

Is there a way to also include the username when registering and logging in via GD?

If GD would also go with the common login via username, it would be wonderfully compatible, since it also uses WP users, and thus it would not be a problem to register via GD, but login in a forum or profile via another Login widget.

Thanks you,
Tom