[Imp]

In the case of the USA air defence would be aimed more at missiles and drones what else is it likely to go up against?

Why worry about an air defence that would only be used against a near peer force the USA has bigger problems despite being a manufacturing giant, it cannot make enough bullets to meet current demand.
Imagine if we had a real war trying to build missiles etc to meet demand, huge economic crisis very quickly especially for the US way of waging war. Rocks could become the new tech.
Europe is in no better position not enough equipment and nowhere near enough ammo it would be gone in a week or less for a lot of armies against you know who.