Which parts of that article relate to loudness normalization?
First, there is digital signal processing software, which is used to accurately measure dynamic range, peak-to-peak, peak-to-mean, and calculate average loudness in advance of playback... as well as apply correction (up or down) to music levels or specific frequencies.
There is also mention of how simple loudness controls work.
Third, there's a good explanation of equal loudness curves which is where things come together for the listener.
These explanations go beyond the OP's question (equal loudness on or off?) but might help him/her develop a deeper understanding of the subject in order to make up their own mind on what's best for them.
A great deal influences what we perceive to be "louder". Sometimes it is peak spl, other times it is the spl at a critical frequency, etc. DR range can also play a role, especially on highly compressed tracks. Many rabbit holes to follow.