'It's a Harrier replacement so is therefore a success if it carries more than the Harrier' argument
One of the mistakes (IMHO) of procurement is the assumption that a replacement has to be better?
This inevitably equals more expensive, more complex...with the downside of fewer units and more down time, and/or greater maintenance requirements (e.g. Merlin)
The advantage of a more capable item, can easily be offset by the reduction in numbers you can afford. I read somewhere that, in comparitive terms, the cost to the USAF of a single F16 was the same as over fifty P51s... pitch 50 Mustangs against a single F16 in a dog fight and you're going to lose a few, but I think we all know the probable outcome?
(facts not checked... but it makes a good story and illustrates my point perfectly)