Oh sorry, I dont know. I use game keyboard+ from locnet for remapping inputs for exagear rpg. It works almost fine. I tried others with my razer kishi, but all have some kind of problem. I own usb-c gamesir like you, but i dont use it often, i prefer razer kishi, probably because gamesir has swapped button A with B. The only thing what always worked (or was possible to fix) across numerous gamepads, keyboards, android consoles, touchpads and various exotic devices which people owns and use for playing is magic dosbox’s own mapper.
But you are right, i did not implement automatic conversion of all gamepad events. Maybe it can be improved, but it will never work for everyone and every game. Probably you expect that left joystick on your gamesir will be converted automatically to 2-axis ms-dos joystick, but in other game you may need it to mouse, wasd, arrows or other dos specific stuff.