Toggle between two usb cords with a 2 pole 2 throw switch
I'm assuming it needs to have data + and - hooked up in order to regulate or cut power once the power bank is fully charged; is this true?


Highly unlikely. Most power banks are simple battery charging circuit's that just happen to use usb connectors, and have no usb related logic or hardware. Most of the time the usb data pins are left unconnected. This may be different for newer QC capable adapters.

Your controller is a different story. It definitely has some usb logic. Unless the xbone controllers only use wireless for data and usb power for charging. Either way, a 4 pole switch mat help, but is not ideal. Usb is a high speed differential pair signal and adding in the switch can disrupt it badly. Usb switching is normally done through ICs designed for switching these high speed signals.