I have a video file on my Android device (One Plus 7 Pro). I use the app AirDroid to download this file to my desktop computer through a web browser or application on the computer. This all happens locally, I can cut the internet connection in the middle of the transfer and it will not impede the transfer.
I find that this transfer is slower than I would expect. The fastest speed I have been able to achieve is 6 megabytes per second, which I only achieve when I host a hotspot with my phone, and connect the desktop to that.
If I connect both the phone and the desktop to a WiFi router, I only get roughly half that speed.
Both these devices are capable of both uploading and downloading data much faster than this. If I connect them to a sufficiently fast internet connection through WiFi, they can upload and download files from and to the Internet at multiple times the speeds mentioned above.
If their hardware are capable of that when transmitting to/from the Internet, why can they not do the same thing locally? I would assume that having removed the bottleneck of the Internet connection, the speed would be much faster.
I have noticed that this speed limitation also occurred with other apps that did similar things, such as ShareIt. I have also noticed it a multitude of Android devices from various brands, and various computers.