The point about the World Cup is four-fold. First, it's about the stage. It's a one-in-four-year event. It remains the biggest tournament and occasion on the planet (even on a forum full of big-club fans like this one). It's the grandest stage to showcase your talent. Second, it's not necessarily about the standard but it's about the more challenging environment. While a well-oiled club side has two world-class players for every position, trains together all year round and can financially outmuscle 99% of its opponents, an international team doesn't have those luxuries. So influencing players who you only play with every couple of months and achieving something when you might have a couple of weak spots in your team becomes important. Third, international football generally stays the same over time. There are more nations competing and more games now, but effectively the big teams are as big as they were a quarter or half century ago. That's not the case in club football where the biggest club sides have become so powerful they routinely mop up 90-100 points a season (whereas a decade or longer ago a league was won with 70-85 points). The reduced competitiveness means it becomes harder to compare achievements in the club game from one generation to the next. Unless you're from a diddy country, then international football is a better way of comparing across generations. Fourth, when you get into the rarefied territory of these greatest of all time discussions, where the performance level is so incredibly high in all competitions, the standards by which these players are judged become more demanding. All of the players in that discussion - Pele, Beckenbauer, Maradona, Platini, Ronaldo, Cruyff, Zico and others - did sensational things in both the club game and the international game. Rightly or wrongly Di Stefano probably doesn't feature in the Pele/Maradona/Messi debate purely on the basis of his lack of a compelling international career. Yet like Messi his club career is as dominant as they come.
I have Messi in that top bracket. But all of that context above, and in other parts of the game, makes comparing across generations very difficult and actually proclaiming anyone as a cut above the rest frankly impossible to do.