The single thing I find the most stifling as a game designer is controller support. It's the thing that most makes me want to simply quit team based game development and make truly tiny indie projects. I hate that the vast majority of games have to work with two low precision stick inputs that you can't use while pressing the majority of the buttons on the gamepad. I hate how it's been shifting my favorite genres into worse and slower versions of themselves for decades. I hate how I simply cannot make design and input decisions without filtering them through a control scheme that happened to stop improving the moment it became almost usable for previously flourishing PC game genres.