What the author also doesn't seem to realize is that while writing an engine you don't have to actually write everything. A lot of times you'll have some library that does exactly what you want and only needs a little wrapper to match your formatting/structuring/concept standards. This way you can gain a ton of functionality really quick and from the final users perspective it's pretty much indistinguishable that there was "cheating" involved. This also allows for cherrypicking topics one actually enjoys spending time on.