I'm not convinced that the top poker players of the past were always the most intelligent people. Perhaps other factors such as experience, stamina and aspects of character (eg emotional stability) were more important. With basically only one book on the subject and limited shared knowledge the most successful players were probably those that focussed on ways of finding and exploiting the fish.
However, in the modern game, intelligence is just the starting point for the top levels (not all intelligent people will make good poker players - a certain kind of mind is required). There has been an explosion of poker theory and knowledge. Modern players have had opportunities to experiment and develop rapidly online among a much larger professional player pool. Intelligence is not a well defined concept but widely accepted aspects of it are definitely important to poker success, e.g. pattern recognition, rapid number crunching, information assimilation, interpretation of complex situations with many variables. As time moves on I suspect such attributes will become even more critical to top level success.
Intelligence is not the same as academic success (although there is obv a strong correlation). I doubt Viffer has ever made it into the top academic circles but he has a certain perceptive ability which means he could take the wages off any professor at the poker tables.