That's a very good point. Turkey is obviously the odd man out on the buyer list, and it seems like a clear case of economic and political considerations clashing with the military rationale of only selling to firm (and easily-defended) friends.
I think it extends the metaphor to NATO very well actually. A mutual-defense alliance gradually turned into a political and economic alliance, and now it's not clear how well the original proposition can be trusted. RAND, at least, thinks Estonia and Latvia can't be actively defended and couldn't be retaken without bombing campaigns in Russian territory. So suddenly, the strength (or at least universality) of that agreement becomes an open question.
I think it extends the metaphor to NATO very well actually. A mutual-defense alliance gradually turned into a political and economic alliance, and now it's not clear how well the original proposition can be trusted. RAND, at least, thinks Estonia and Latvia can't be actively defended and couldn't be retaken without bombing campaigns in Russian territory. So suddenly, the strength (or at least universality) of that agreement becomes an open question.