I think Home Assistant is powerful for device control. HomeOS is more focused on family coordination (tasks, shopping, notes, schedules) rather than smart home automation (although my vision is to add device controls too). But the main reason I built from scratch is the flexibility so that I can shape it exactly how my family wants it. We changed the entire theme to a warm colour palette because my family preferred it, added prayer times because we needed them, and built the UI specifically for a kitchen touchscreen. That kind of control/flexibility is hard to get when you're working within someone else's platform.