Except 1, 2 and NV are all fairly consistent and then Bethesda just took a big shit on them.
I think it depends greatly on your definition of consistent to be honest.
* Why have the Vault Tribals reverted to primitivism after only a century?
* Where did they get a gigantic stone temple?
* Why has Shady Sands abandoned its spiritual beliefs to become a secular expansionist nation?
* Why did they change the Vaults by making them social experiments?
* Why would the Vaults make social experiments AFTER a nuclear war?
* What happened to the Nevada Rangers who seem nonexistent in Nevada?
* Why is New Reno not mentioned in New Vegas?
* Why would Arcade Ganon still be alive when all of the children in the Enclave would be on the oil rig?
* How is Caesar's Legion able to fight NCR when they don't use most modern weapons?
* Why does NCR have to rely on the Followers of the Apocalypse when they have Vault City and the Shi?
* What happened to the Shi's plans to bloom the desert?
But if it works for you, yes, that would be exactly what I am defending. It doesn't matter because it's a good story.
I get what you're saying, but you're talking about a crossover spin-off. I'm talking about actual entries in a series being consistent with its origins.
I'm mostly flexible about these sort of things as I mention above. For me, Fallout 3 is canon because I love the game and I think people should have the option of disregarding it if it doesn't fit their view of Fallout because it's all personable.