You lose about 30% efficiency using "standardized wiring" with an inverter heat pump instead of a communicating thermostat, because running a heat pump at 33% power continuously instead of 100% power 20 minutes of every hour results in a COP about 30% higher.
They don't need it, they just don't get all their rated efficiency, which is much higher than single-speed systems. Single-speed systems commonly have cooling efficiencies around 10-14 SEER, the Gree Sapphire is 38 SEER. If you ran it at only full power, it'd probably only be 30 SEER.
