Hey there. A couple of things that need to be taken into consideration.
There is nothing odd about the life cycle analysis to me. Norway estimates a $300 million cost per plane per 30 year life cycle and the US estimate 460 million per plane per a 55 year life cycle. That seem pretty consistent!
The assessment that the F-35 can carry 6 missiles is accurate too. The block 5 plane which is the version that the Norwegians plan to accept into service will be able to carry 6 missile internally which is the same as what a Air-to-Air configured F-16 with 2 drop tanks can carry which seems reasonable for a plane that is designed a F-16 replacement.