Wars of attrition are won with factories, not bullets. The US manufacturing capabilities can no longer compete with all nations, and they are likely to continue that downward trend. Combine that with war machines that are very complex, and you have a very limited production speed.
The top tier equipment is often overpriced for what they deliver, and can't be rapidly replaced. The F35 is a good example. Super expensive per unit because it is a multi-purpose craft. Meaning it's not quite as good as a bomber, and not quite as good as a fighter, but way more expensive than eaither. I'm not even sure if the US has the capability to make one by itself. There's just no way they can 'pump them out' if it faced real adversity.
They are powerful aircraft, but they have a low power to cost ratio, and are exceptionally difficult to produce.
It doesn't matter if the F35 is able to take out 5 enemy craft for each one lost, if the enemy craft is 1/10th the cost and time to manufacture.
In a practical sense, China probably has the most dangerous air force. Each individual plane may be a shitty knock-off, but they can produce new ones faster than the US can mobilize existing forces.
Same, to a lesser extent, is true with Russia. Russia is often closer in ability though. The SU50 could (though probably not) even be a superior plane. It is more capable in maneuverability and radar detection, so who knows.
I think the US military has also realized this. I think that it the real impetus behind the light attack project. It is not just about saving cash, it's also a means of sustainable warfare. I think it will continue with light designs for other roles, as well as land and sea versions of the program.
I agree if we're talking sustained warfare, but any of the three countries could destroy the next if they didn't have to worry about the third one getting them. The threat of open nuclear war is the only thing stopping a sustained land war. Well, that and the fact that China and the US are completely economically codependent.
Keep in mind that if one of these countries decides to invade the other, it wont be a land campaign like WW1 and 2. The opening move will most likely be a covert cyber attack on the power grid. Sleeper agents would use the cover of the chaos to sabotage key infrastructure. While the infrastructure of that country crumbles, civil unrest will begin, military personnel will abandon posts to protect their families, fuel will stop being delivered, and after a few months the weakened country would either be divvied up between the other two, or just left to rot.
As you said, "Wars of attrition are won with factories, not bullets." So to win that war, you take their factories.