The F-35 requirements have not been tightened - indeed if you call cost and schedule requirements, they've been relaxed.
The problem was always that they set out to do everything for a sub-F-16 LCC. Unfortunately there are no chapters entitled "Bibbedy-Bobbedy-
ing-Boo" in either the works of Adam Smith or Theodore von Karman.
EM - You can't offer a price until someone writes a requirement that you can meet. As far as I know the Cloggies have never done this. So to that extent Dassault is being honest. They also apparently said this week that they would only play if the ground-rules were open.
This is sensible in view of the Noggies' action in 2008, when they pretended to have a competition, and than made up lots of growth factors on Saab's fixed-price offer while accepting LockMart's moonsh... I mean, optimistic predictions like Holy Writ.