I understand that. However everywhere else it took maybe a week more and only for the first few months.
Does that really explain why the US is still having these problems? My guess is that the system is overwhelmed either way. Flights from and to China also were massively less, yet the worst delay we had with china was like 1 week. And today it is on average a week less than before Corona, because most postal systems were actually able to grow and better themselfs in that time.
Didn't help that people bought more and more online and would order inter-continentally if they had to (I know I did!).