I don't think you can posit the theory because the idea of "appropiation" wouldn't apply to the casting of a mainstream film franchise, especially if the casting was done by the studio that owns the rights to the film franchise.
I don't see anything in my post that implies endorsement of a non-zero-sum creation. That's only partly because I don't think there is any such thing. From the standpoint of tallying race, there's no ostensible difference between casting a minority in an existing property and creating a new property for a minority star. Which would be more successful? Obviously an established property is a safer bet.
In case it's not being picked up, I'm using a conceptual vocabulary employed by British cultural theorists, most notably, by Stuart Hall and Raymond Williams.
The "non-zero-sum" creation of character (e.g., like a Bond) is a "win-win" because it can appeal to diverse audiences in diverse ways. So, e.g., it's possible for in-group white-Brits to secure feelings of identity and pride from Bond's encoded white-Britishness (which is, I take it, the source for the uproar over Elba's possible casting, which would strip Bond of this characterological essentialism), and it's possible for non-Brits enjoy the appeal of Bond's other traits like his swagger and proficiency, which, make no mistake, is still tied to the character's encoding, but is enjoyed by out-group members who find that character and his encoded traits enjoyable -- a win-win. As you write, "you can enjoy the film without even considering [Bond's cultural and racial encoding]." Yes, one can, but just because one is not aware of what one is enjoying, does not mean that what is going unperceived is not a huge part of the pleasure one is experiencing.
Moreover, the "taking" or "appropriation" of the Bond character (traditionally white), and its subsequent "giving" or "assignment" to a black actor can be done by the film rights-holders, whether they're white or black. The issue is one of erasure, namely, the emergence of black-Bond (encoded to give birth to Bond's new "blackness") at the expense of white-Bond.
Again, I understand this idea to be the source of the controversy, and, take it or leave it, I'm out on the subject.