It doesn’t help that a lot of Chinese packages come in poly bags, which are a lot harder to OCR than a flat box or envelope.

But intl shipping is based strictly on weight, so senders have every incentive to cut weight wherever possible.

I don't see how poly bags offer any weight advantage over an envelope. The advantage they have is durability: paper envelopes get easily ripped open, whereas poly bags are nearly indestructible for about the same weight and size. I've also noticed that many shippers now print their mailing/customs label directly onto the poly bags, so that probably makes the shipping process faster and more automated.

China had postal 2D barcodes for more than a decade...

Guys in the video seem to be showing the pile into sorting machines.