Correct me if I'm wrong, but ultimately the energy requirement for flight boils down to optimal lift-drag ratio, doesn't it? My impression was that we were in a

Correct me if I'm wrong, but ultimately the energy requirement for flight boils down to optimal lift-drag ratio, doesn't it? My impression was that we were in a pretty sweet spot there already, and can only expect marginal improvements (higher aspect ratio (which comes with its own challenges - from airport suitability to structural stability), less zero-lift drag by reducing wetted area). Even if we double L/D (which would be a substantial achievement, no?), battery-electric flight would only have endurance of about an hour with current tech, and then maybe 2 hours in two decades after specific energy has doubled again, just about giving us a bit more than 1000 km (after reserves etc.).