Not too many people want to take the docking station with them out on the field.

A fast computer does not automatically solve the latency problems in the USB interface. Just about any serial port solution should be able to handle a huge baudrate without data loss. But when you have a solution where you must be able to toggle the handshake signals quickly, it really does matter how much latency there is in the hardware layer.

With a "normal" transfer, the handshake signals can be handled in hardware by the UART, but a number of older solutions are using the hardware signals for other things - such as resetting hardware, or acknowledging data or similar. They where implemented at a time where the hardware layer itself had hardly any latency, and possibly in MS-DOS or Win95 where the application could busy-loop and directly access the hardware controller to avoid the delays induced by interrupt handlers and Windows driver stacks.

Keeping an old machine is always a good idea, but it can be quite expensive to get new batteries for older laptops. If it is enough to buy a card with a "IBM PC-compatible" serial port then it is often a good choice to try. The serial port will always work well. The only limitation is that Win2k and forward will still not be able to match MS-DOS or Win95 for handling the decisions.