Two zone hvac on single compressor
Prior to variable frequency drives (most people call inverters) having 2 compressors was the most efficient system out there but the cost was quite high so many just oversized the compressor these systems 2 pump have longer life if well sealed because the compressor job is split up.
All heat pumps that I have seen have a reversing valve this reverses the flow of the “Freon” or refrigerant so instead of removing heat from the house it is removing heat from outside and using that heat on the inside. This is why heat pump efficiency drops off depending on the type and age efficiency roll off starts at ~24f but some newer high efficiency models can run all the way down to -5F.
The only problems I have found on 2 compressor multi zone systems is the control boards die and can be quite expensive. Some of these units are 20+ years old and only needed a recharge when they were having problems (other than the controller)
So your system appears to be a high efficiency model of its day and was quite expensive so I would not mess with it unless something is broken.
Running a big compressor all the time will cost more. The small compressor costs less to run but is not large enough to push 2 heads especially in heat mode.