Most useful thing they could have done was make the port on the case USB-C as well. Otherwise I actually agree with OP that a USB-C to lightning cable is pretty useless as I still need a separate charging block to use it rather than get dual use out of my MBP charger. I hope Apple fully transitions to USB-C happens sometime soon.
I don’t want a USB type C on the case ... that would require me to carry another cable just for that. I carry with me the Powerbeats pro , the AirPods pro , bower and Wilkins PX5 AMD my iPhone. The bower and Wilkins PX5 has enough of a charge I don’t carry the cable and I don’t use them that much tbh. The Powerbeats is for work where I prefer the hooks and the AirPods are for bus travel