In fairness to the author, he is rightly pointing out that maximum efficiency is pretty much irrelevant, certainly in audio-type applications.
He's also rightly pointing out that class-D isn't necessarily as efficient in real-world applications as the marketing/hype would suggest.
In the real world, class-G, especially with the inner transistors in class-B, can be surprisingly efficient and vastly lower distortion than any class-D.
FWIW, various combinations of class-D and switched/pumped/tracking supplies have been around for decades in things like loud-audio radio-pagers.
This article contains an number of errors. The theoretical maximum efficiency of a class A amplifier is 25% for a singled-ended stage, and 50% for a push-pull stage. Similarly, it can be shown that the maximum efficiency of a class B output stage is about 78%.
What are the engineering and design challenges in creating successful IoT devices? These devices are usually small, resource-constrained electronics designed to sense, collect, send, and/or interpret data. Some of the devices need to be smart enough to act upon data in real time, 24/7. Are the design challenges the same as with embedded systems, but with a little developer- and IT-skills added in? What do engineers need to know? Rick Merritt talks with two experts about the tools and best options for designing IoT devices in 2016. Specifically the guests will discuss sensors, security, and lessons from IoT deployments.