THERE we go. finally. Turns out that using Xinput is better for the 8bitdo sf30 pro with Rpi3 because sure you can set it to Dinput mode, but Retropie natively reads it as the 8bitdo sf30 pro, and... then it ignores the existence of the Star and uh... moon??? buttons, meaning you have no usable "hotkey" button. :|

so you gotta make it think it's a 360 pad ahahaha welp