The nasty bit in all this is that it appears the car did have FSD at the time the OP looked at it, and it was only later revoked. This is pretty bad (well, awful really) on Tesla's part; if they are going to de-content a car for resale, they should do it before they part with it
Somehow I missed a bunch of posts in this thread. I think they were coming so thick and fast!
Having seen the window sticker and Tesla's dated response about removing features after they had sold the car, all I can say is I don't know what more the OP could have done. Only with hindsight can one say that at the first sign of features changing before completing the transaction, the OP should have said 'not buying until car has exactly features I'm expecting', but even if that had happened, or if Tesla had been a little slower in removing features, the question would still stand 'can Tesla make good on corrections to specs especially using OTA after Tesla have sold the car.'? (obviously involving downgrade in spec).
My choice was to buy directly from Tesla purely to reduce the risks exposed here and make it a slightly clearer transaction were things to go wrong.
Have there been any similar situations when LFUSC started getting stripped by Tesla? Clearly there are cases where cars were sold / pex' d with lifetime free charging, that would have transfered to subsequent owners, but then the game rules got changed by Tesla for their benefit and to the loss of some dealers holding cars and affected owners.
And the question that clearly needs addressing is what Tesla's rights are if THEY sell a car with certain features active and with no way of a buyer being able to find out reliably if and how the stated spec could be incorrect and potentially change in future.
If you can't trust a car sold by Tesla to be sold correctly, then good luck to buying through any other source.
Legally, it sounds very tough to wind the OP's situation back, other than by a good will gesture from Tesla.
Last month I bought a food mixer. The one that arrived was a deluxe version of the one I paid for, and when I called the seller to check if they wanted to correct the mistake they just said 'sorry, our error. Keep the one we sent you.' OK, the OP didn't buy a food mixer, but neither would it sink Tesla if they did the right thing and made good.