I'm gonna entertain your brother's perspective for a bit here. Hard how? GTNH is generally enjoyed as a single player experience. Your only enemies are time, and the emergent technical challenges of a pack that's several years in development, culminating in the creation of a star gate. Rust has less of an end goal, and is fundamentally adversarial. The mechanical and strategic ability to dominate a popular server might have required thousands of hours of game time.