Ok. I think you are trying to wrap sense around things that are never explained that way. Like you're putting more thought into it than Bethesda ever did.
Who in the game said there's thousands of old foods lying around for the taking? That there's anything left to scavenge at all after 200 years seems like a simplification for the sake of gameplay more than anything (so that the player has anything to gain from scavenging outside of raider bases).
The soil is not poison. There are animals that live off it.
They do not have fortified walls nor high-tech weapons, they have garbage that a behemoth could headbutt out of the way. And places like The Republic of Dave just have a chainlink fence. As I said, the only place that looks remotely defensible is Rivet City. They don't look all that concerned about defending themselves.
There are places in the West Coast such as the Boneyard (Los Angeles) that got bombed to hell yet have people living in them by FO1. The effects of nuclear bombs are not that widespread and longlasting, even in the FO universe.
They do have GECKs in the East. They have a dozen vaults spread around, each with 2 GECKs. There's only like 4 vaults ever that didn't get a GECK. All they have to do is go in and take one. Instead they're sitting around like morons, too busy collecting vintage nuka cola bottles.
Also radiation is very different in this setting than in reality. It's one reason everything is nuclear-powered. Heck, I don't think ghouls are a result of FEV... Just magic radiation doing weird nonsense. A lot of them were turned when the bombs dropped, long before the FEV started spreading. AFAIK.
Not really. The FEV spread when a bomb directly hit the
West Tek research facility (later known as The Glow). Although it's somewhat disputed whether ghouls are a result of plain 50s pop-scifi radiation or radiation mixed with FEV. The latter makes more sense (and is stated as canonical in the Fallout Bible), but the former is what the original creator envisioned.