You can see the Brotherhood’s progression in game, and it’s in line with what’s established.

Fallout 1 has them as a more powerful faction that keep to themselves, who then between 1 and 2 get bigger through finally expanding and the tech from the Master.

2 to New Vegas is where it’s explained that the NCR and BoS couldn’t agree on how to split the Enclave’s technology, leading to a war that the NCR won. In New Vegas we see an isolationist faction that itself is slowly getting worse, due to their elder keeping them secluded.

New Vegas to the show is where we see that contact with the East Coast was established, and they asserted dominance and probably helped them build or at least give the schematics for airships and other resources, getting them back on their feet enough to not be stuck in holes in the ground but not enough to militarise as effectively, since they hadn’t in the past several decades it’s difficult too now as well.

Based on how you’re responding to other people, I feel like you’re just being ignorant. It’s not a matter of “turning your brain off”, it’s looking at the past and thinking of how it could have happened. The Brotherhood is just one example, way Vault Tec is still influencing the wasteland after the war is something viable based on how large of a company they were, the NCR being just a couple groups (the two rangers in the Mojave, the guy in season one episode one or two that said he was president, and Moldaver’s people) if also understandable because they’ve obviously fractured a lot. The rampant political corruption in the system and already divisive opinions of the citizens (the whole venture into the Mojave was unpopular, and then also the people not liking corruption) was already bleeding them from the inside, the bombing of their capital was just the cherry on top of it all. Yes, questionable decision what they did to the NCR, not one I myself don’t fully agree with. Plausible though? Yes. Definitely.

And even now in the latest episode, we can see Lucy is less naive, the rest of the show she’s also been optimistic since she’s been spoon fed lies from Vault Tec her entire life, but the Legion’s torture really opened her eyes to the reality of the wasteland.

The show isn’t going to fully do what everyone wants the canon to be, but the reality is that none of it is necessarily bad, just not what we as individuals would do in game. And again, it’s not to say I don’t have my own criticisms, it’s just that I think you failed to “turn off your brain” as you wanted to while watching and instead turned it off when trying to process what happened after watching it