Igaro C1 does ~10W to USB actually, but it's 1.5A + 500mA to the second port. You can see it doing 1.75A in a reddit post @ https://www.reddit.com/r/bikepacking/comments/1fvhoj3/review_igaro_c1_dynamo_light/

There's no such thing as 5W to USB, the USBv3 specification is 900mA. However for USB-C CC there are only the two modes (excluding the 3A mode); 500mA and 1.5A, so if USB-FL comes with USB-C it'll have to register as a 500mA sink, so 2.5W regardless. The C1 automatically switches between the two and reconnects the USB devices to reestablish the best current (since USB spec doesn't have dynamic power).

As you say USB-C PD isn't a benefit for dynamo hub power, the slight efficiency gain in the cable is reduced as users generally use short cables say from the light/charger to a phone/gps on the handlebars, and the boosting of the voltage internally has an efficiency penalty.

I thought IQ-XL might also have USB but actually that is/was an assumption. My bad.