I do agree it is a tedious process. But I understand how it came about.
We've been using Garmin GPS devices since 2005. Garmin has never been good at software, neither on the PC nor on the GPS device. Their user interface used to be awful but has gotten better over the years. If you think poorly of the Clarity map update process you should have seen the software 10+ years ago. The search algorithm in the GPS devices, and the Clarity, sucks big-time by being slow and not finding strings within strings.
The way the PC software works for handheld or dash mounted GPS Garmin devices is you bring the device to the computer and plug it into a USB port. They simply took that same approach with the Clarity but you can't bring the device to the PC. So they designed the work-around to plug the USB thumb drive into the car essentially making the thumb drive the GPS device. Once the thumb drive is plugged into the PC the Garmin software treats it as a GPS device. Clunky and time consuming but it works.
I must say though that Garmin is a to notch company when it comes to support. They have been very responsive with me the few times I needed support. Their software is clunky but it does work.
I used a 32GB thumb drive with similar times reported by others. I had to sit in the car for about 20 minutes with the car on which sucked. The car, initially fully charged, actually went back into charge mode after sitting in the garage switched on for those 20 minutes.