Again, this goes to show why the Brotherhood Crusaders should have been Catholic. We know the Catholic Church survived the apocalypse in one form or another (there's the Church of Saint Monica in FO3's Rivet City, which is a Catholic Church run by a priest, and in FNV, Benny's gun Maria is a blatant nod to Our Lady of Guadalupe) and even if they didn't, some disillusioned Brotherhood unit could have found a book full of Catholic teachings and/or a Catholic Bible and adopted Catholicism along the way.
Mormons don't like Cross symbiology, but most mainstream Christian denominations, Catholicism included, use it all the time as a symbol of Christ's sacrifice for the sake of mankind's souls. Not to mention the fact that the real-world Crusaders were a Catholic religious/military movement, and Roger Maxson himself formed the Brotherhood after being inspired by the scribes and knights of the west who preserved the knowledge of the west after Rome fell-CATHOLIC knights and scribes. So a renegade Brotherhood of Steel outfit fully adopting Catholicism isn't out of the norm, when the Brotherhood itself was inspired by Dark Ages Catholic knights and scribes preserving what scraps of Roman knowledge they can get their hands on.
Considering how edgy the NCR campaign was, the devs were just a bunch of unimaginative slobs who simply wanted to make their own fanfic take on FNV. But unlike most FNV fans who know the lore, these yahoos barely touched upon it. I knew it the moment they had you kill wounded NCR soldiers after the Helios One battle. The NCR would never do that. The NCR is many things, but they're not that kind of straight-up evil. At most, the soldiers would all be on stretchers, many of them might bleed to death, and some might even request to be killed instead of living on in pain, but they'd never resort to just shooting their own wounded soldiers without their consent. That, and the large number of vertibirds and tanks on the NCR side-that's just pure bullcrap. It would have made more sense if the Frontier NCR was actually a renegade Enclave op that went native and took in deserters from the NCR to boost their manpower, and they decided to rebuild America their own way up North, which would explain where they get all the cool shit from.
The Enderal devs managed somehow. They came out with their mod 5 years after Skyrim was released. They came out with a unique game of their own in 5 years, while it took the Frontier devs 7 years to make a bad CoD ripoff that raped Fallout's lore to hell and back.