That's not the point. You are assuming the fighters are only for use against the US. There is the possibility of Brazil (or any other country that has bought

That's not the point. You are assuming the fighters are only for use against the US. There is the possibility of Brazil (or any other country that has bought F-35s) getting into a diplomatic tiff with the US, losing access to their fighters because of it, and then being unable to use them for standard training exercises or boarder enforcement against neighboring countries. Having your fighter fleet grounded would be "disappointing" in far more situations than "is in a hot war with the US".