It seems the USB-C port on Osmo Action only gives USB 2.0 speeds of 20 Mbyte per second, at least that's what I get connecting it to my macbook pro via usb-c to usb-c cable.

The card in Osmo is capable of 90 Mbyte per sec transfers. That is kind of pathetic.

All little cameras make up for poor mass storage devises, you should get a nice USB 3.0 or 3.1 card reader,,,, provided of course you have support for that on your computer.
On my home wifi i also just get 300 mbit, and really my phone wifi which i have used for the test should be better than that and i have 1000 mbit at my disposal at the modem.
I am myself looking for a new card reader as the micro slot in my current Kingston one are worn out after only a few years, and my new motherboard / computer give me the option for the very fastest USB and not just USB 3.0.
AND ! never go down on hardware

I'm actually super disappointed at the slow USB-C speeds. I upgraded from a GoPro Hero 7 Black to the Osmo Action and I love just being able to bring my iPad or MacBook and a single USB-C cable. But I was surprised when I tried transferring just 25gb of video to my computer and it took a HALF HOUR! My GoPro was quick so I guess I just expected it to be the same. It's not a dealbreaker but nobody wants to bring additional equipment when it's not necessary. This is the first true negative I've run in to with my Osmo Action. Hopefully DJI will address this issue in the 2nd gen Osmo Action. Also hoping for wireless charging so it's always topped off and ready to go!