As far as I can tell the duty issues over the last 2 years is resolved. The current duty for most assembled PCBS from China to USA is 35%, and this is what I've paid on orders in the last 3 months from JLCPCB. One order was DDP DHL and the other was CPT DHL.
CPT DHL, dhl charges ~$20 of brokerage fees, slightly cheaper but there is a chance that DHL doesn't use the correct HTS code and rate, which would require email /phone discussion, fix the paperwork, deliver delayed a day or two.
DDP DHL, jlcpcb charges ~$40 of brokerage fees, usually stuffed inside the shipping charge, the 'duty' will be 35% of merchandise. Slightly higher (hidden) brokerage fee, but more certainty on the duty rate, since it is listed during the payment
Some HST codes will be higher than 35%, and some product descriptions could trigger higher rates (in my experience). For example JLCPCB has 'battery charger' as one option for the product description. Since JLCPCB only makes pcbas, not full modules, then this "battery charger" could only be the control board for a battery charger, which would be 35%. But "battery" text could trigger high rates, which can be corrected back to 35% but would require contacting importer/broker. This is known/common issue with UPS, they seem to use the highest plausible rate instead of contacting the customer for clarification.
using fourfathom's numbers:
pcb $66.32 + assy $1302.52 = 1368.84
customs $479.11 / $1368.84 = 34.99%