Couple of things to note: There are 3 (I think now 4 if you include the one in Indianapolis, IN) warehouses in the US that stores iphones (MT, Juliet, TN (Geodis), there is one in PA (can't remember what the name is), there is also one in California (again might be Geodis or something else). That thread you link, that poster indicated that he/she tried to order for launch day but due to connections, that poster got it delivered late. So not a launch day.
Once supply and demand catches up, any phones will then be stored in the warehouses and eventually if you order it it will be shipped from one of those locations. I bet you if you had ordered one in January of 2023, that it will come from a warehouse and not from China.