I do believe in Santa Claus. I do I do I do. And flying reindeer. And rainbow-pooping unicorns. Any of those are more likely to be real than an APS-C sensor that's as good or better than the 5DIII at high ISO.
In a fight between physics and fantasy, my money is on physics.
I don't disagree with you about sensors, but still, be careful betting all your money on it ...
"Heavier than air flying machines are impossible."
-- Lord Kelvin, president, Royal Society, 1895
"The resistance of air increases as the square of the speed and works as the cube [of speed].... It is clear that with our present devices there is no hope of aircraft competing for racing speed with either our locomotives or automobiles."
-- William H. Pickering, Director, Harvard College Observatory, 1910
"Even considering the improvements possible...the gas turbine could hardly be considered a feasible application to airplanes because of the difficulties of complying with the stringent weight requirements."
-- U. S. National Academy Of Science, 1940
"Professor Goddard...does not know the relation of action to re-action, and the need to have something better than a vacuum against which to react....he only seems to lack the knowledge ladled out daily in high schools."
-- 1920 New York Times editorial on Robert Goddard's rocket work.
"The energy produced by the breaking down of the atom is a very poor kind of thing. Anyone who expects a source of power from the transformations of these atoms is talking moonshine."
-- Ernest Rutherford, 1930
"This foolish idea of shooting at the moon is an example of the absurd length to which vicious specialization will carry scientists. To escape the Earth's gravitation a projectile needs a velocity of 7 miles per second. The thermal energy at this speed is 15,180 calories [per gram]. Hence the proposition appears to be basically impossible"
-- A. W. Bickerton, 1926
"Fooling around with alternating currents is just a waste of time. Nobody will use it, ever."
-- Thomas Edison