I think that the term is made up and irrelevant from the get. It was made up as a marketing tool to promote Ray Robinson. In this day and age it is meaningless because skill has taken a very very back seat to the ability to manipulate dehydration/rehydration limits to create advantages. Physical advantage has replaced skill.
For what it is worth, I rate Benny Leonard well above Ray robinson as the best, 'pound for pound', because Robinson was a 6 foot tall lightweight,welter, and middle, when the heavy weight champ was barely over 6' tall. In other words, his 'incredible skill' was very much aided by physical advantage. Benny Leonard had no physical edge. he was the most skilled fighter of all time.