I feel like the core gameplay is like the main storyline of a novel — you start by focusing on a single point and then branch outward from there. A simple core mechanic reduces cognitive load, allowing players to instantly understand the game and enter a state of flow. After that, the extra side mechanics are like scenery along the roadside — they should only be added after the main corridor has been built. I feel like games like The Witness or Dark Souls were made with this kind of approach in mind. Of course, this is just my personal opinion.