However...if you want to take your light aeroplane on a long distance trip, then burning Jet is undoubtedly better. I know of someone who took their DA42 from the USA to South America and did a tour down there before flying home....something next to impossible with Avgas. For us in Euroland, the same applies....
I am sure the same was said about Diesel cars in the past, and if you look at the USA ,in California you can't even buy a Diesel VW which does 60 MPG , yet you can buy a crappy new petrol Mustang which does 20 at a push (and has a 3 speed gearbox). Every second car in Europe is a diesel, it is efficient, and is the norm (and arguably better), and the technical advances are light years ahead of the old skool US cars with diesel engines running half a million miles without batting an eyelid.
But I agree, if you fly where Avgas is available and priced correctly then there is not much incentive at the moment. I do think it is time for these gas powered Lycomings to be controlled by FADEC though which would improve efficiency and also engine life and make them easier to fly.
Trouble is someone has to be first to buy this new tech....I would if I could afford to, but I can't.