But, they absolutely are. PS5 and Series X are filled with old technology - inefficient x86 CPUs, optical drives, expansion slots, and the massive power supplies needed to feed them. Not to mention the massive heatsinks, heatpipes, and fans. If Apple's efficiency claims are true and they can match a desktop PC class CPU with mobile wattage, and they can do the same with graphics - all of that *bulk* can fall away.
The Series X's mainboard is a rather small device. It's just all that other *bulk* that turns it into a monolith