With the U.S. and other nations spending billions on developing and building a new generation of stealth aircraft, there is still a lot of uncertainty about how effective stealth will be in combat. Over the last two decades there have been many efforts to come up with effective ways to spot stealth aircraft and bring them down. In 1999, the Serbs used a number of these techniques to detect and shoot down an F-117. Since then several other methods have been developed, and the U.S. Air Force says it has developed countermeasures. The problem is you will never know if these work until there is an actual war involving stealth aircraft going up against creditable air defenses manned by clever personnel. One has to be particularly careful going up against the Chinese or Iranians.
Another lesson to be kept in mind is what happened with radar (BVR or Beyond Visual Range) guided air-to-air missiles in 1991 over Iraq. While 1991 was the first air battle featuring large scale use of BVR missiles. What was not mentioned was that most of those missiles that took down a target did it at close range, where a heat-seeking missile could be used.
It was also not reported (at least not vigorously) that unguided (dumb) bombs were still sometimes a cheaper weapon for getting the job done. Carpet bombing of enemy ground units, even those with a lot of armored vehicles, was very effective and much cheaper than using guided bombs. In fact the most cost effective aircraft for taking out ground targets were the A-10 (which the air force has been trying to retire for over two decades) and the F-16 (a very flexible and low cost aircraft designed mainly for air-to-air combat). All this means that foes not equipped with the latest tech but with well trained and aggressive pilots can be a real threat.