I understand what you're saying, but those are all self-inflicted vulnerabilities from trying to "nation build".
> It's of course important to prepare for a larger scale war against China, Russia, etc. but realistically we're more likely to be fighting a handful of goat herders in Afghanistan with an AK and a bag full of rice before we're taking on an armored division.
Broadly, I think there are 2 theories of conflict.
The first is what I'll call the "justice" theory of conflict: people fight because they are oppressed.
The second is what I'll call the "rational basis" theory of conflict: people fight because they think they can win, or because their backs are against a wall and they have nothing to lose by fighting.
IMO, the second theory has much, much more explanatory power.
If you buy the second theory, then the major reason there is no war between the US and China or Russia is because they don't believe they can win (which is probably true, as long as the US doesn't try to invade). But in order for that to continue to be true in the future, the US needs to continue to invest in military assets that are effective in fighting near peer opponents.
It is also important to be good at fighting developing nations. But ultimately, being good at that doesn't matter as much. If the US goes home from Afghanistan, that might affect the Afghans, but it doesn't really have global implications. But a hot war between the US and China would result in a truly enormous number of deaths.
Also, I don't really see much evidence that the US has ever really been successful at nation building. The last real success was South Korea. And it's just as easy to see that as a fluke rather than the result of US presence (during the peace - obviously the US helped immensely during the hot part of the conflict).