Manned fighter aircraft were clearly the most effective weapons platform for the past 40+ years and are likely to be the most effective of the next decade. Beyond that their cost effectiveness is in doubt.
The USA and to a lesser extent Russia have clear dominance over any likely enemy when it comes to air power. However if we learn the lessons of history we can see that other countries are looking at ways of nullifying this advantage.
In the same way that air power made Battleships irrelevant in WWII, we should expect other countries who cannot hope to match the power of the USAF to look to missiles and drones to defend themselves.
Developing and maintaining drones and missiles that can swarm against manned fighters is something that many countries can hope to achieve. These countries know that they could never train or maintain a manned force capable of resisting the USA. This leaves them with the choice of either surrendering to the demands and whims of Washington & Moscow or developing/buying a capability to deter attack.
The future drones don't need to be as good as a highly trained western pilot in the latest fighter, it just needs to present a serious risk to said pilot. This risk that can be increased by the fact that the drones/missiles will be much cheaper and probably expendable in combat situations.