> For a hybrid system to be worth it, you need to claw back more efficiency than you lose in going from mechanical energy to electrical energy, and then back again.

For short-haul you spend a lot of time climbing and descending in relation to long flights, so the plane spends less time at the optimum the engines were designed for (cruise), so, if the power unit can be at the peak efficiency throughout the flight, with extra energy being supplied by the onboard battery for take-off and the power unit be shut down for descent, we might get to a point where it's economically viable, depending on battery operating costs and weight.

You are right to point out the aerospace industry has tried everything conceivable to see what sticks, but technology evolution sometimes throws us a curveball.