I can only guess fuel-consumption-to-thrust efficiencies (longer flight times) or pure cost since a pure gas turbine will always beat out a mechanically linked

I can only guess fuel-consumption-to-thrust efficiencies (longer flight times) or pure cost since a pure gas turbine will always beat out a mechanically linked fan-stroke in specific power (i.e. kW/kg), but will almost always be more costly due to the extremely high manufacturing tolerances required for turbines.