Not necessarily. The RTS/CTS pins on the serial port are there for the device to tell the host "stop sending data, I need to process the data already sent"

The reason this doesn't work is that USB adapters don't have those pins, and thus assume you can send it at 30kbaud - not respecting when the device says it must pause sending data.

By introducing a static flow rate below what the CPU can handle, it should theoretically keep the flow rate below the threshold that the CPU starts to choke at