You are, as usual, confusing fact and opinion. There is no definitive empirical way to prove that one player is better than another, so it's a matter of opinion rather than fact. You can often say something is 'near enough' to a fact because 99.9% of people will agree with it - for example that Messi is a better footballer than your mum, or that your mum has had sex with more men than Messi has - but if others on a football forum disagree with you about which of two players is better, then it's not only not a fact, it's not even a rarely disputed opinion - it is instead a matter of opinion on which people hold contrasting opinions - sometimes opinions that many people would deem valid, other times opinions that seem batshit crazy - but opinions rather than facts nonetheless.