Are you saying that, as Bitcoin doesn't have a publicly stated problem definition, its immune from any criticism of its design choices? That's a bizarre argument.
First off, Nakamoto's original paper has a section on Privacy, talking about how to maintain privacy by keeping public keys anonymous. If Bitcoin, in practice, fails to provide privacy for its users, it is absolutely fair game to point that out.
Secondly, perhaps you mean that the original paper didn't have a formal specification of the 'privacy' desired, which the performance of Bitcoin can be evaluated against? Again, that's a bizarre argument.
Lets say I release a new design of car. You build one and drive it, and then it goes on fire due to a design flaw. How would you feel if I argued "But I didnt formally specify the parameters within which it wouldnt go on fire and injure you!"
That'd clearly be a nonsense argument, because there are expected standards of operation of a car, even if there isn't a formal spec. If you write an informal section on privacy in your paper, and your system compromises user privacy, criticism is absolutely fair.
> if you want that hypothetical system to not have this "linking" property, whatever that actually means.
The "linking" property is well defined in the context of Bitcoin anonymity; I refer to the situation where multiple addresses used as inputs to a transaction reveal the shared ownership of all those addresses.
As Nakamoto writes: "Some linking is still unavoidable with multi-input transactions, which necessarily reveal that their inputs were owned by the same owner."
