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'm not sure this scenario would ever occur. From the 50s onwards, the kind of conflict that would involve troops landing on US soil has not been viable. Wars involving major nations are fought diplomatically, with quiet attacks on infrastructure or through limited warfare in "third party" nations.
If it did happen, I'm inclined to agree with you, at least in the short to mid term. I think the US would need to be extremely cautious in the way military assets were used. China and Russia's militaries are the way they are because they've been constantly playing catch up for decades. The US has had a lot of time to make a bunch of shiny and impressive war toys that are highly advanced, but not suited to manufacturing at a rate needed during war time. Russia has also started doing this, but to a limited extent in comparison to the US, due to the difference in military budget.
I think it is quite difficult to predict what would happen in terms of military advancement. There are tactics developed by the end of WWII that are still applicable in conflicts today, for example, so what would the playing field look like after 5 years of war between major nations today? (Assuming nuclear weapons weren't used, which I do not think would be the case). There is a strong case to be made that it might not even be a war of attrition. The destructive power of even conventional weapons is far superior to anything used in a major war up until this point.