GameSetAndMath said:
When we are talking about "the best player to have never won a slam", surely a huge weight should be given to player who had come close to winning a slam and/or whose games are known to cause trouble or at least stand up to the favorites. To me, that is more important than other achievements like total number of titles or even number of Masters title.
But see, now you're narrowing the definition beyond what the thread title says: "Greatest non-Slam Champion of the Open Era." Let's unpack that:
"non-Slam Champion" is easy - a player who never won a Slam.
Open Era is from the French Open in 1968 to the present.
The whole thing hinges on "greatest," which is an open-ended term. But I think it makes more sense to look at it broadly than to narrow it down like you did, as in "the player who had the best chance of winning a Slam but didn't." That also opens the door to other factors, like era and competition - which a player cannot control. For instance, Albert Costa won a Slam in 2002, in the weak era of the late 90s and early 00s, and wasn't the player that many on that list were or are.
I hear the argument about Rios, but I find his Slam record far less impressive than Ferrer considering that Rios peak when Sampras was slipping, while Ferrer was/is at his best during the era of the Big Four.
So I think the question of the thread relates, or should relate, to greatest player as a whole - that is, based upon career achievements. We can then look at numbers and come up with an answer, like I did with my formula. Another question might be, "Who was the most talented player never to win a Slam?" That would be more subjective.