All of this is of course highly dependent on the type of contract the part-time flying is based on. There are advantages to 10-20% reduction below normal working time as it will become easier to roster crews because cumulative duty time and rest times are less of a concern. Below 70-80% advantages start to be outweighed by the non-diminishing fixed costs (proficiency check, recurrent training, uniform, etc.). For long-range flying or rostering based on long trips part-time may make it difficult to roster according to the part-time factor (I.e. if you are supposed to fly 50 hours and long-range trips have around 20 each, you can either fly too little or get overtime.
We have had part-time flying including forced part-time to weather a previous crisis for over 20 years and crewmembers appreciate having it as an option.