afaik: those mainframe type screens do have different fields embedded, only you can move with the cursor keys inside each field and between the fields. if it's one text widget, you can type over or insert text right over your username/password labels or delete them entirely. so if a user makes the mistake of typing over the labels username/password, how are they supposed to know where the input area for those is?
Yes your completely right and dispite my natural enthusiasum I am beginning to see that I am no match, in the time I have, to take on 30+ years of hardware software intergration by massive corporations. I'll probably return to an entry box solution, but its been fun trying.