By that standard, every nuclear-armed aircraft ever built, and all of the ICBMs ever built, are "useless". Ridiculous.
But that's not even the point. Since the Raptor has become IOC, there hasn't yet been a conflict where there has been an air threat, and hence there hasn't been a reason to employ it. It has nothing to do with "refusing to expose it to a combat environment." Use a hammer to pound a nail and a screwdriver to install a screw.
If that's not the point, why bring it up? It seems that every response that you have is terse, rude, and snarky. If you are asking a real question to get my opinion, a certain degree of respect, and courtesy may fare better for you. If you're just asking these questions rhetorically, I'll take them as such and move along.
So....based on your crystal ball, what "REAL airborne threat" will the US "ever face"? I mean, since you seem to have some miracle wisdom about that, I'm sure there are lots of man hours and money to be saved in not training to fight Flankers and wade into IADS of double-digit SAMs.
The point isn't if anyone in the world can match Raptor -- clearly they can't. The point IS if anyone in the world can match the aircraft it's replacing, and there are numerous air-to-air and surface-to-air threats that are widely fielded that will absolutely make mincemeat out of Vipers and Eagles. That's true today, and of much greater importance is that it will especially be true in years to come.
Let's not forget the lead time required to design, build, test, and field an operational combat aircraft. The Raptor took more than 15 years to go from paper to operational status. It's not like we can whip up a new batch of capable airplanes in a few weeks once a threat starts showing itself. The Viper and Eagle are OLD designs. It's like the Wright Flyer was sitting on the ramp at Wheeler Field the morning of 7 December 1941 instead of P-40s.
All of this is a moot point, anyway. Raptor is here in operational service...it is phenomenally capable...and they'll do whatever they need to in order for it to be healthy for decades to come. God only knows there's no replacement for it coming anytime soon, either.
Here's my answer, and I'll answer assuming you are asking why I see things the way that I do. I have no crystal ball, just a good measure of perspective and experience to draw from.
There is nothing on the horizon that hasn't been announced in terms of the "latest and greatest" Gen 6 fighter. The military industry needs politicians to do their work. The politicians need the defense companies to do their work, and the politicians can't keep their mouths shut. It's why the JSF was announced before the first CAD image had been drawn. Sukhoi's latest and greatest is the Flanker. Name an operator of the Flanker that you are scared of, or even respect as an adversary. Honestly. Is a Viper in the hands of a Pakistani the same as a Viper in the hands of a Zoomie? An Eagle in the hands of a Saudi the same as one with our guys in it? We know the answer to that...
Anything that IS being kept super secret squirrel renders you, the pilot, obsolete, anyways, and that's just the way things are going. We live in a new day and age.
We aren't going to war with China. They own us. Like all of our debt own us. And all of our manufacturing. And the majority of industry. They'll default us, and it's game over. Russia? Pakistan? N. Korea? We would have done it already. Who is it? Iran? It won't be because they pose a real threat to yours or my freedom.

If the argument is that we needs them to counteract SAMs, why are packages built around Growlers and CJ's? The F-22 went into service in 2005. Why was it sidelined for Iraq?
As I said, we're in a new age and time. We have no clearly identified enemies because they are groups and factions, not nations and states. We have the ability to deal with them with our current assets.
We built the F-22 to keep Lockheed in business, and to maintain a technology baseline. That's really my opinion, and the above illustrates why I think what I do.