Even if Shahade's argument makes some sense, it totally falls apart at the amateur level. No one can improve without slow chess. They just have no time to think and notice what they're doing wrong that they can reasonably fix in 30+5. The glaring flaw in Shahade's whole thing is that people love classical chess, because it is the only place that you can really unlearn some things and learn others.
And if Shahade doesn't want to grind out 10-hour days, he doesn't have to. He can do that however often he wants. That's no excuse for fixing something that isn't broken.
My humble opinion is fast chess is more for casual players who don't want to spend a lot of time over a chess board. After all i think chess is still the thinking mans game and not as much as for the nimble and fast with their hands. Its only possible to work out a very quick sequence of moves if one has already some familiarity with a prepared or familiar line, but for someone who is just working on his skills, its too discouraging or daunting to keep on losing because you fed your pieces including your king unwittingly or by the slip of the mouse or fingers.