AFAIK most American AC units can be retrofitted to be heat pumps pretty easily. You’re just making it flow in reverse, after all.
In automotive at least, it’s pretty common to size the evaporator and condenser coils based on their expected operating temperatures and (therefore) pressures. Usually this means condenser is a lot bigger than evaporator.
If you reverse the flow with the right valves and compressor setup, then the heat exchangers will still be sized wrong for efficiency. I suppose you could design a bidirectional system from the start that trades off for middling efficiency in both modes.
I’m not at all convinced that there are a substantial number of such bidirectional-sized residential systems installed in North America. But it’s also possible that the residential folks don’t care much about HX efficiency.
That makes sense, but also most heat pumps I know of are also AC units - like those mini splits installed in new apartments these days.
Would that not also be a balanced system?
And even if we’re talking about lower efficiency it’s still more efficient than burning gas in a furnace right?