Unfortunately it does not work that way.
The USB to RJ45 adapters you see on the commercial market are design as signal repeaters, with a 2nd USB to RJ45 adapter used on the other end.
Those adapters are used to extend USB cables past there Recommended 8 to 15 feet length. The USB to RJ45 is not a raw 4 USB pin to pin 8 RJ45 configuration, the signal is also modulated to take advantage of the RJ45 8 wires and electrical impedance of the cat 5/ cat 6 cable. So the adapter translates USB protocol to something that works better on a Cat 5 or Cat 6 cable before allowing the other end translating the signal back to USB protocol.
The $12 USB to RJ45 cables you see for sticks are all custom made and has the pin out (on the RJ45 end) to match PCBs such as the Cthulhu, Kitty, Cerberus or PS360+
The RJ45 connector is just there as a cheap 8 pin solution for multiple cable swaps, and USB protocol is being sent though with out any changes.
One last thing, you do get what you pay for, this applies especially with arcade sticks.