Yes RC doesn't need any USB stick for FW update. Those old procedures are obsolete, where did you read them.
Per new procedure, DJI Go App when connected to Internet will let you know if any updates are needed. RC update can be directly done by clicking the update link on DJI Go App for RC. Wait until all is done and then reboot RC.
For AC update, you need to download bin file and use it on SD card. Wait until gimbal led turns solid green.