The main point of conflict is that the US holds the source code for the advanced software systems very closely, no partner country has access. A lot of the differentiated and exotic capabilities of the F-35 that make it attractive to other countries are in the software, everyone recognizes this. There are many algorithms and techniques that rely on classified computer science to deliver qualitative advantages. Even if other countries could replicate the hardware, without replicating the software anything they built would be a pale shadow of the F-35 in terms of capability, which makes alternative hardware much less compelling.
The US knows all the leverage is in the software, so that is the part they strictly control. It is yet another case of the software eating the world, military systems edition.