I think you’re right, in that Fermi problems give you a rough sense of what’s going on, and an estimate that’s generally good within an order of magnitude. (I did google a couple of numbers, but not much more than that.) The value is that you can get that good a sense of things without doing much research, spending much time, or even doing too much arithmetic.

To get a tighter estimate would require a much more detailed understanding of the details, and I’m sure this is a complicated topic, well outside my sphere of expertise. Hopefully you find out something interesting!