76 takes the cake, and not just because it's the latest, newest addition. 3 brought people into the series, 4 was the pinnacle of the mass-adoration, Shelter a shameless cash grab, but 76, ontop of being a buggy mess that maniacally shoves and slaps on 'fallout' everywhere, also hurt the perception of the series (at last) and might actually have real ramifications for Bethesda. The fanboy has a limit and 76 crossed it. 3 nor 4 nor Shelter did that.
Fallout Tactic's plot was, to me, simple enough. Some BoS Radicals get sent out west basically just to get rid of them; if they succeed then the East Coast can bring them back to heel somehow, and if they don't, they're dead. But we're the plucky BoS and we're not gonna take this shit so we use our military might, discipline, and arms to bring law to the wastes, beating up every threat until we're the only ones left. It doesn't help that beyond Raiders, you have a beastman-empire, then Supermutant remnants, then a robotic pre-war warbot autofactory ramping up to kill all biological life on Earth. The MwBoS did their share for the world, for sure.