I find it particularly odd that my file uploads to Dropbox transfer 10X faster than my file transfers from my USB stick to my hard drive.
It's called the back door boost. 10X faster when uploading to NSA servers!
It must be a more complicated process than it seems. I have PCIE4 NVME SSD x 3 in raid 0 (all on their own x4 lane), and it’s not as fast in practice as in measurement. A ton of little files is somehow very different than a few large files.