!Posting to answer my own question on the off chance it helps someone else later down the line!
I’ve made my game mode, I’ve made my controller, and I’ve made my pawn. I’ve set up the most SIMPLE of events on them. Events like “Press F print Hello”, or “Begin play print Hello”.
I’ve correctly assigned them in the Project settings, and I’ve correctly assigned them in the World Settings JUST in case. I’ve saved a half dozen times.
Upon playing, Character controller still wont receive input. Basic events still wont fire. Pawn isn’t even spawning or being possessed!.
… open your game mode blueprint class, and hit compile. Yes I know, it has a green tick, but you still need to do it anyway, once that’s done, it will all magically work.
It would appear that if you create a new blueprint asset, and assign the default classes from directly within the asset, the compile icon will automatically change to the yellow question mark as expected, but if you assign the controller/pawn to the game mode via the project menus, the compile icon will falsely display a green tick. Not sure if bug or working as intended.