4k Airmen is a pittance, but they need it...DESPERATELY! I think I can understand the acquisition of more F-35s now that they have come to grips that it is not a CAS airframe & are focusing on having it be the replacement for the F-16. I think they will need to focus on getting more F-22s as the F-15 fleet ages out.
The lack of bonuses for pilots will not help the shortage. Although, there have been surveys done that show that not even hefty bonuses would help the shortage as the most prominent issue with pilots (and the Force in general) is toxic leadership forcing good Airmen out because they can't get promoted unless they have noses up butts so far that when the leader picks their nose, they're picking for two.