I believe the OP's point was that the math described in the article is too simple and not enough to do any serious research. Anyone who attempts to do NN research already knows this material (and a lot more). This tutorial could be useful to someone who wanted to implement simple backprop from scratch, but all DL libraries already do it automatically. Someone who just wants to learn a bit about NNs to classify images or generate text does not need to know this, and someone who wants to make a breakthrough in NN theory already knows it. So yes it's not very clear who is the target audience here. I'm guessing it's for a bright highschooler who just learned calculus and who is interested in how NNs work. For such students I'd recommend reading http://neuralnetworksanddeeplearning.com instead.