What this boils down to is how much money do you have and how can you spend it. One of the first things you take a look at is the Bartlett Model which is a circular model: Strategy > Tools > Risk > Goals > and back to Strategy. Between Strategy and Tools you have the input of Resource Constraints (basically, the size of your Defense Budget) and between Risk and Goals you have the input of the Security Environment (what is the threat?)
As for strategy, what is it going to be? Primacists (the most money - maybe 6% of today's GDP), Cooperative Security, Selective Engagement, or Isolation? Which one will the voters support and Congress fund?
It all comes down to money and how to spend it. The F-22 is a fine machine - but is it a higher priority than other items? How many air to air kills have we had in the last 10 years? the last 20 years? the last 30 years?
We studied this in the NSDM (National Security Decision Making Course) at the Naval War College. It was a course on threats, budgets, strategies, the acquisition process, etc. With the F-22, the F/A-18 E/F, the JSF, and the MV-22, - not to mention funding for Navy ships, the Air Force 767 tanker deal, the increase Army buy of H-60's, the Corps H-53 and H-1 upgrades, we are going to have a train wreck on funding. We simply can not afford everything.