According to a Valve Engineer, the Steam Machine specs outclass the most common PC configurations. The company relied on its own hardware surveys to choose the system’s components. Even as an entry-level option, Valve claims that 4K/60 fps performance is realistic, despite a memory-limited GPU.
I think Intel’s issue is that they’re focusing on the low end. Anyone with a 3060 or better would see the b580 as a lateral move at best, or more likely a downgrade. A b770 card would probably have gotten me to upgrade as long as they weren’t stingy with the ram.