The gigantic failures exist so that when there is an actual need for aerospace engineers to respond to an actual threat, rather than the theoretical projections based on the data from the last war, it won't take 25 years to train them up from scratch.
The failures are not quite as horrible when you realize that it could be more expensive in the long run to do nothing at all. But then the questions turn toward the amount of pre-emptable core capabilities we need to maintain. For a long time, the doctrine in the U.S. has been the ability to sustain simultaneous nonnuclear war in two separate theaters plus nuclear second-strike capability sufficient to create a MAD deterrent. That is expensive. And since we haven't actually needed that much war materiel since 1945, that leaves a lot of room for waste.
It could be argued that the limited regional wars of choice that the U.S. has pursued since then have simply been capital maintenance, to prevent the military from decaying into expensive uselessness. I think in its deepest backrooms, the generals still gauge their effectiveness by whether they could fight both Russia and China at the same time.
I understood it to be a bit more specific than this: sustain conventional war against our two strongest non-allies.
In any case, it's also my understanding that we've been maintaining a level far higher than what would be required for this.
Look at the Iran-Iraq war for the level of casualties that some potential enemies are capable of taking (half a million fighting age males dead on Iran's side). North Korea having 9 million military age personnel brought up in a personality cult. Let along China and the size of their armed forces.
The USA lost four thousand in Iraq, two and a half thousand in Afghanistan. The UK lost nineteen thousand men dead on the first day of the Somme in 1916, do you really imagine a Western nation losing that many for any conflict today? To be honest even in a war of national survival I doubt it.
We lack the political will to sustain conventional war. The military knows it and acts accordingly.
Your reply seems focused on the quantity of soldiers. This is an important factor, but I was primarily considering overall spending, which obviously includes lots of capital expense, logistical stuff, etc., aside from the personnel. I believe that the level of investment in military hardware and the like is significantly higher than would be required for a successful war on two fronts (assuming that there exists such a thing as "successful war" these days).
It's why the Iranians had over 1 million casualties taking on Iraq. And several years later, the US rolled over the Iraqi military with 1,000 causalities.
So sure, the US can't successfully invade China, but it would sink the entire Peoples Navy and defend Taiwan, Japan and S. Korea.
We don't do that anymore... Because a full total war is too expensive -- when the US suffers a loss of 20,000 men in a day, a button will be pushed in a silo somewhere and cities will vaporize.
That's why North Korea exists today.