Where would you put user filter modules? We go back and forth between system and input. Additionally, a module such as where a planner selects whether they want to plan in USD or Local Currency (A pick list)
From a DISCO perspective, functionally both would be okay as either System or Input would serve a similiar purpose in terms of flowing information downstream to Calculation and Output modules. Personally, I would classify those as Input modules as End Users (i.e. not model builders) are making inputs and adjusting the reporting and presentation of the Output modules. I view System modules as fairly static reference modules like time reference, mapping definitions that do not change often or only changed by workspace admins, things like that!