It is mathematically impossible for flying (or rather hovering, to be more precise) vehicles to be more fuel efficient than ground vehicles.

I mean think about it from a physics standpoint. A flying vehicle needs to constantly expend energy to overcome the force of gravity pushing it down. A ground vehicle only needs to overcome friction forces, the main one at slower speeds being friction between the ground and wheels. It's the same reason why pushing a cart to carry heavy loads is easier than carrying something by just lifting it in your arms. It's why wheels were invented.

That ground friction is even lower when you are looking at a train where the point of contact of wheels on the rails is much smaller than rubber tyres on asphalt. And it's even lower for maglevs, where the main friction is air drag. In general the rule of thumb for energy efficiency is: Trains > Automobiles > Planes.

Of course the advantage of flying vehicles is that they can generally get from point A to point B faster since they can go in a direct line, which saves a little bit of fuel, but mainly it saves time. So this will be a convenience thing, and making it economically viable from an energy standpoint requires you to have cheap and abundant electricity. This is also why we haven't seen personal flying vehicles take off as a commercially viable option until now with the progress we've made in EVs and electric batteries. Because if it was powered by fossil fuels it would be far too expensive.

Well...that and the advent of machine learning opening up the possibility for developing adaptive software which allows drone-like flying vehicles to maintain stability and fly autonomously or semi-autonomously.