Given how similar it sounds to that of a Tesla Model S + SpaceX - Battery, Electric motor, propeller and such, Why wouldn't Tesla attempt such a thing based on components they already build for Tesla or SpaceX?
VTOL will get less back because it's grossly inefficient.
Note that drag needs to be deducted from the potential energy. There's parasitic and induced drag.
Given that the aeroplane ends up stopped on the tarmac at (approximately) sea level with (approximately) empty tanks, how so? A bit of heat I suppose but that's not usable. I'd say current aeroplanes generally deliberately dump energy to the environment (via deliberately increased drag, spoilers etc.) during descent, no?
I think that compared to energy expenditure X in level flight at cruising altitude, the aircraft would expend X+Y in the climb and a little less than X-Y in the descent, assuming all horizontal distances are the same.
To the extent that they deliberately increase drag, that wouldn't hold true, but I'm guessing that's mostly on final approach.