Probably the two best modern militaries in the world right now are Ukraine and Russia, not even kidding. Experience is just so fucking important in running an army that everyone whose senior enlisted and officers aren't experienced and tries to fight a war just turns it into a shitshow, at least for the first few months until they get their heads on straight.

The most recent real combat experience the US has had was in Fallujah, twenty years ago. Everyone who fought in that is retired now, and everyone currently in the military with combat experience either only has experience acting as glorified police officers or doing special forces crimes and there's not nearly enough of the latter type to fill out the whole military.