I think you're exactly right, that fubar is fouled-up-beyond-all-recognition, or sometimes, a different f word beyond-all-recovery. This I learned during my 26 years with the US military. 9 Army, 17 Air Force.
Following Hillary Clinton's disaster in Benghazi, Libya, where she received fairly clear warnings, but chose to ignore them, ending in disastrous results, we started to hear the term "fugazi."
The old Vietnam era acronym had been updated after Benghazi...
This has come up quite a few times and continues to be a point of confusion. In the books Irving is clearly described as a white man. However, in the casting for the Amazon series they cast Lance Reddick as Irving. Reddick does a great job as Irving and after seeing him it is hard to imagine Irving as anyone else. It's just one of many differences between the books and the series. This Wiki deals primarily with the books. Details about the series are included under the Portrayals section.