Stealth has been a major game changer!
If you're referring to a conflict such as the US war in Afghanistan, or the Conflict in the Balkans in the 1990's then yes stealth was not a major factor because the defending sides could not wage a real "strategic" or "high tech" Air or Electronics war in return. In a situation like these wars an F-16, A-10 or Harrier is good enough to wage a limited air war. The Serbians did have SA-2's and SA-6's, ZSU-23's, etc. but the capability of these weapons, and their numbers were very poor. Sure the US, France, and the UK lost several aircraft to Serbian fire over the coures of 5 years but this was in no way a losing attrition rate.
In the 1991 Gulf War, and to a lesser extent the 2003 invasion of Iraq, stealth played a huge role in the outcome of both conflicts, the F-117 was able to destroy Iraq's ability to communicate, and destroyed the very centrally controlled Iraqi air defences in the opening hours of the war. Yes many equipment and radars remained operating, but the capability of Saddam to wage an effective defense was gone! Stealth was a huge morale dropper as well, and the Iraqi military already had very low morale in 1991! In 2003 the Iraqi air defences were still capable, but no where near the level that they were in 1991. Obviously once the Strategic air campaign was over in 2003, stealth did not matter as it shouldn't anyways in a war against insugents but to achieve the strategic victory over Iraq Stealth was once again was a deciding factor.
There has not been an aerial conflict with these circumstances in which stealth has been involved with since 1991, and the Stealth capabilities of the F-22 far exceed the F-117 and B-2.
There are alot of factors to consider when determining what technologies and tactics will achieve victory. When it comes to a "real" war with both sides possesing advanced and capable equipment stealth will always make a difference.