Why? Have you seen all the top level players of all time, to compare and make a judgment?
If you want to argue he was the best player in the last ten years, then I'd agree he was, by a short head over CR7, but (a) no one remembers far enough back to evaluate all the players and (b) the way the game has changed makes comparison difficult.
Also, Messi has played his career in a league where there is a concentration of good teams at the top and rich pickings against the others, thus goals galore - yes, you can only beat the team in front of you, but it's a factor in judging greatness, as is World Cup performance.
Compare Messi with Mardona in that respect and the latter has a far superior record - Messi is, however, a far superior sportsman.
I've been watching football since the late 60s and would judge Pele the greatest in that period, factoring in his tremendous World Cup performances, with Maradona second and George Best in third (mainly because he didn't play in the World Cup, not because of his skill level - he was the best all round forward I have seen, when interested).
Names that crop up as 'greats' from the 40s, 50s and 60s include di Stefano, Puskas, Garrincha, John Charles, Stanley Matthews, Telmo Zarra, Valentino Mazzola, Jose Manuel Moreno, Adolfo Pedernera. I didn't see any of these people play, but the anecdotal evidence is strong.
There will be good shouts from the 20s and 30s, too.
So no, it is neither funny nor absurb to say that I am unsure if Messi is in the top 10 of all time, as it is impossible to judge that - I was reacting to the sweeping statement, not deriding Messi, who is a great player.
I didn't write that Messi is not one of the top ten players ever - please review my post. I said I wasn't sure if he made the top 10 (because there are decades of players I did not see, who are also said to be fabulous in their time - I'm told that ). Clearly he is a great player and could well be in the top 10, I am just not sure through lack of knowledge. People I know in South America say that Argentina's three greats are (in order) Jose Manuel Moreno, Diego Maradona and Messi - I saw Maradona, but not Moreno. Maradona performed much better in the World Cup than Messi (as well as cheating, which Messi has never done, to my knowledge - he is a sportsman and a fine opponent) and that is the reason he gets a higher ranking - you may disagree, that's fair enough.
Having seen both Best and Messi, George was seamlessly two footed, as good in the air as CR7 inch for inch (though the latter is taller and thus more effective) and had the same blistering acceleration, as well as being nearly impossible to dislodge from the ball when dribbling - he will never be rated as highly as Pele, as he didn't play in the World Cup finals and that is the ultimate arbiter in the eyes of many. For me, Best was a more all round skilled player than Messi, but that is my opinion - Messi has been a more dedicated professional over whis whole career and is totally top drawer.
Messi has scored a ton of goals in La Liga, but what would Best have achieved if playing for Rangers in the Scottish League Division 1 in the 60s/70s? Pele scored a bucket load domestically, but Gerd Mueller had a fantastic record in the Bundesliga, as well as for the West German team. Context is important.
BTW, Pele played for Santos, not Sao Paulo. Having spent time in Sao Paulo, I know this for a fact.