One thing to remember- the various USB standards have a transfer rate of XX-- as the standard becomes newer the speed increases. But It also depends on how fast the actual device is, and if it has some sort of buffer or cache. Some devices can deliver pretty fast transfer rates, such as SSD drives. Others might support the latest standard (USB 3.1 I believe) but the device itself cannot feed the data as fast. Slow memory cards on a USB reader are one example of a device that may not live up to expectations. USB 3.0 is pretty common over the last few years, but many really cheap devices might only support USB 2.0.
Think of a nice fast road where the speed limit is 100 mph, but your car can only achieve 70 mpg at best. If you had a more powerful car, you might achieve closer to the theoretical max.
USB 1.0: 1.5 Megabits per second (Mbps)
USB 1.1: 12 Megabits per second (Mbps)
USB 2.0: 480 Megabits per second (Mbps)
USB 3.0: 5 Gigabits per second (Gbps)
USB 3.1: 10 Gigabits per second (Gbps)
I stumbled across this article which actually seems pretty good and covers Ethernet, Bluetooth, Wifi , Thunderbolt and Firewire and other network devices. One of the things I hear frequently is people complaining about "something slow"- like Bluetooth. This is mistaking the comm / network / protocol purpose, and trying to squeeze out something for which it was not designed. Bluetooth is low power, quick to connect, and cheap to implement. But it is slow and short range, and has a limit to the number devices on a segment. https://helpdeskgeek.com/networking/a-breakdown-of-file-transfer-speeds/
Wikipedia on USBhttps://en.wikipedia.org/wiki/USB
I was looking at the history of USB, because I can remember before USB, SATA and even ethernet were introduced (remember Arcnet, Token RIng, or gawd-hep-us something like RS-232 ?