WC is the greatest prize. anyone disputing is a fool.
Something being the greatest prize is different than something being the greatest measure of a player's talent.
Usually, those two things would go hand-in-hand. The best way to measure a player's talent is in competitions with the highest level of play. And the competition with the highest level of play is almost always the greatest prize.
But in football this does not hold anymore. The World Cup used to have the highest level of play. Combined with the fact that it is country vs. country, it became the greatest prize in football. It remains the greatest prize as a historical anachronism and because of the fact that people will always care more about country than about club. But it does not exhibit the highest level of play anymore. Rather, the highest level of play is clearly in the Champions League.
So while people may care about the World Cup more, the Champions League is clearly a better measure of a player's quality.
And that is not even mentioning the other huge problems with using the World Cup as a measuring stick. First off, a tournament involving only a handful of matches for each player every 4 years has such a tiny sample size of matches that it is virtually impossible to glean anything from it. Secondly, players cannot control what country they are from, and different countries have wildly different quality teams, so players' success in the World Cup is HEAVILY affected by exogenous factors.
Decades ago, those problems could be overlooked because the World Cup was still, by far, the highest level of play that existed (and also the only thing widely televised). But now it really seems silly to me to use the World Cup as a dispositive factor in judging a player. It actually boils down to a handful of games every 4 years that are played at an inferior level.
Ultimately, I think the World Cup's biggest use now is in judging a player's "clutch" factor. Did they repeatedly step up in a tournament that people really care about (i.e. Klose)? Did they repeatedly choke? These things could alter one's view of a player. And I think one could sort of argue that Messi has choked in the World Cup. At the very least, he hasn't shown his best. Of course, he also made multiple game-winning goals this last time around, got his team to the finals, and was one of the tournament's better players. So, personally, I wouldn't say the dip in quality is stark enough to label him a choker due to his limited sample size of WC performances. This is especially true when one factors in the fact that he has been an affirmatively clutch player in big matches for his club.