Barca would be 3rd best in the world if Messi didn't play for them.
Strongly disagree with that. In fact, I think they'd still win La Liga without him which is the strongest league in the world for me. Barca's style of play is one that doesn't rely on one individual near as much as many teams. They wouldn't be quite as free scoring, because Messi is the best finisher. They would still score very often, and they would win most of their games the same. Even if they dropped to 3rd in the world, that's still pretty damn good.
A little off topic, but I'm gonna use basketball as an example. As a kid growing up, everyone told me Michael Jordan was the best player ever. For most of my youth, I 100% agreed with this. Now, there are people saying Lebron James is better, and he is the best ever. The clash of generations is the biggest separation in opinion. Now, I would say Jordan is still better than Lebron, but I wouldn't say either are clearly the best ever. If you look at the history of the NBA, player like Kareem Abdul Jabar, Wilt Chamberlain, Bill Russell, etc. must be considered. Chamberlain for one was hands down the most effective scorer in NBA history.
Back to football, it's really the same. The current generation is all about Messi at the moment. Part of it is just popularity, but there is a large part of him performing at a very high level. The thing is, when you look at history you see Pele, Muller, Maradona, etc. performing just as well or better at different points in their careers. Saying he is hands down the best is kind of crazy for me. He will be considered among the best ever, but picking him as that outright number 1 is madness.