International mail is aggregated by China post, and they pay the USPS for the last mile.
The aggregation that USPS gives domestic shippers a discount for involves actually doing all but the last mile of the shipping process - taking a large group of packages to the appropriate shipping area. This is a process that would require a shipper to have a fleet of long distance trucks (something large and medium sized US shippers have).
If you're claiming China Post does this in the US, I think you need serious references. And, as I mention above, it ultimately doesn't matter. If China Post is doing this, they would be doing it for free because the total cost we're talking about individual shippers paying, in shipping things from China, is close to the last mile cost that USPS charges domestic shippers.
This is kind of ridiculous, USPS also sorts the packages they receive from individuals. It seems kind of clear that there's no special magic that packages coming from China are going to have that packages that are already in the US are not going to have. The USPS page I link to above specifically says that the USPS prices lower when companies do their work for them. That work is not going to be free.
It's not magic, it's just that the USPS doesn't have to do the work of sorting them.
Labor costs in China are much cheaper than in the US, it stands to reason their cost of sorting there will be less than what the USPS implicitly charges for sorting here.
The aggregation that USPS gives domestic shippers a discount for involves actually doing all but the last mile of the shipping process - taking a large group of packages to the appropriate shipping area. This is a process that would require a shipper to have a fleet of long distance trucks (something large and medium sized US shippers have).
If you're claiming China Post does this in the US, I think you need serious references. And, as I mention above, it ultimately doesn't matter. If China Post is doing this, they would be doing it for free because the total cost we're talking about individual shippers paying, in shipping things from China, is close to the last mile cost that USPS charges domestic shippers.