Design of an airplane (esp. combat one) is a decades long process
If the way the Eurofighter was designed is anything to go by I think such designs can be accelerated rather dramatically by clearing out the idiots and civil servants involved whose contribution mainly consisted of having meeting after meeting to check if nothing was developing that needed hiding to ensure their smooth progression through the ranks of idiocy.
The whole process is screwed. You start with some needs that are usually defined without any input from people that actually have the ability to develop a reasonably acceptable map of what could happen in the future, then you get funding from people who don't care about anything but their next election and how good they look with celebrities, and next you then start haggling with companies whose main goal is to ensure they can underbid each other for a spec they will help to make as flawed as possible so they can reclaim the underbidding by almost continuous change control, which means you always end up paying FAR more than the bidding process the accountants got themselves promoted for.
If, by some weird stroke of "luck" you manage to actually build the damn things you will then face the next hurdle: maintenance, a new opportunity to stiff the poor taxpayers who have zero say in how these experienced gangsters waste their money.
It's a racket from end to end. Delivering an actual plane seems to happen almost by accident.