If I rephrase what you said to make sure I understand it correctly: Cooling costs would be the same as AC units and heating would be cheaper or same depending on the cost of Gas. Would that be correct?
A ground loop can make cooling cheaper too, as can upgrading to newer more efficient compressors.
Down in the comments, sounds like MA has good incentives, but not seeing other states. CA is banning new gas installations, so I assume heat pumps are the only way for new developments
Yeah, kinda. They can convert the incoming power to dc then back to ac at a different frequency so they can run at any speed. This cuts the energy losses from start-stop.
Less related to heat: It also has a neat side effect that it's a very simple change to make them run directly on solar with no (separate) inverter (and with no AC->DC step). On top of being more efficient even with AC->DC->AC this means in hot climates the energy used for cooling is used more efficiently, and the inverter on the solar array doesn't need to be as big (if you're getting full noon sunlight you probably want the AC on).
I can see places like coastal california where you're on AC virtually year around and maybe need a day or two of heat.
Eastern Washington? 10 cents kWH in Spokane.
I don’t know if any coastal Californian locale that needs AC for more than one or two weeks a year. Even in LA you can get by without AC.