I don't think the point is to compete with power grid energy storage, but for cases where the energy must be in the form of aircraft fuel, so it doesn't quite m

I don't think the point is to compete with power grid energy storage, but for cases where the energy must be in the form of aircraft fuel, so it doesn't quite matter if it's less efficient on all metrics that pumped hydro -- unless you plan on running a cord from a dam to the planes.