Your first point seems to be reflected in the article, except that, if they are correct, the high end of Class D amplifiers apparently is not "super cheap".

I don't quite get the aggressiveness of your second point: surely just leaving whatever your first association to a topic is out cannot warrant such outrage? It's not like they present this article as groundbreaking innovation. Not only do they cite other DIY efforts. The whole premise of the article is that the author himself already did this ten years ago,.