Rather great players tend to shine supernova bright whilst surrounded with other great players tailored to their needs. Which happens at almost every top club that has such a great player.
I'm glad you decided to bring that up. At club level a Messi is allowed to always perform at optimum capacity, surrounded by optimum conditions without any control experiment in sight. International football is the perfect control experiment.
Messi is too much of an individual for this argument to be used. He is the greatest and most individualistic talent in the game. He shows this at club level because he plays consistently enough to express this.
In regards to Barca, Xavi and Iniesta benefit from his presence every bit as much as he benefits from the Spaniards if that's what you mean by 'optimum conditions'. People always go on about how Messi benefits from these two, but Xavi and Iniesta owe there domination of a football match as much to the players upfront who manage to retain possession in very tight situations. They'd be running back to prevent the counter all the time without the likes of Messi and Pedro to keep the ball under-control in more advanced areas. Messi, in particular, receives some incredibly quick passing under a hell of a lot of pressure, yet he comes out of it the majority of the time. His ball retention is excellent.
Scholes finds these passes, just as the two Spaniards do, yet Rooney is often unable to control them. This has a massive effect on our team, mainly because possession is swapped at this point, meaning that Scholes has to run back and defend instead of controlling the game like he should be doing.
That's obviously not to dismiss the brilliance of Xavi and Iniesta. However, their job is so much easier having players upfront who can consistently control these passes. Barcelona have it so fecking spot on, here.
International football is very consistent. It's the players who participate who are not because they are taken out of their comfort zones. Which is when we see how good they really are. As opposed to the hyperbolic level club football elevates some of them to.
If you mean in the sense that it usually comes about at the same time every season, then yeah.
However, you've got: managers changing each tournament, tactics changing, players coming in and out, travelling all over the world to different countries (or all over the country or several countries in a world cup/continental tournament), different training methods and different dietary schedules to what players are used to for their clubs....etc
There is far too much change, and not enough of a consistent routine to implement it. Given how much of a science football is, this will have an extraordinary impact on players.
Given this, judging someone's
individual ability is a much better and more accurate process at club level. That's not to say that international football is irrelevant, but it is obviously a less significant factor.
It must be stressed here that we're going off topic! I was trying to make a case against international football; not a case for Messi, in particular.