USB ports have four “pins”; two for power, and two for a high-speed serial data connection. As many USB devices require power and lack external power connectors since they expect the USB port to provide power, you already have one issue.
The other is that data rates truly do take a hit. To give you a hint, here are the bandwidths:
USB 2.0 (currently the most common) = 480 Mbits/sec
USB 1.0 (a decade old and rarely seen now) = 12 Mbits/sec
Parallel port = 1 Mbps (typically)
Serial port = 230.4 Kbits/sec = ~0.23 Mbits/sec
As you can see from the numbers, transfer rates are hundreds of times faster with USB. Some devices can handle that slow a data rate while others cannot, and others will do so with issues. A disk drive will read/write sssssssssssssssssssslllllllllllllllllllllllllllllooooooooooooooooooowwwwwwwwwwwwwwwwwlllllllllllllllllllllllllllllllllyyyyyyyyyyyyyyyyyyyyy. A large file that I could move in a about a minute on USB 2.0 will take me well over half an hour on USB 1.0, about eight hours on a Parallel port, and about a day and a half on a serial port. You do NOT want to use such a connection for data transfer of any notable size. It would work, but not well
Something like a video camera uses enough bandwidth that it would just fail outright. A mouse may act funny; sluggish, and jumpy. A keyboard wouldn’t care unless you type a bazillion words a minute.
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TL:DR version – Just because you can do something, that doesn’t mean you should.