Messi is still one of the 2 best players in the world until concrete proof of the opposite. And as far as i know, we won't see proof of that that soon.
This being said, i am sorry but his presence in the team as currently constructed makes no sense at all.
We all know the squad is going trough a period of reconstruction. The end of an era suddenly hit last season. It's no ones fault. It's natural. Let's stop blaming each other for that.
Messi clearly doesn't fit a team that is rebuilding. Messi needs, and has ALWAYS needed a team with mature performance and at the peak of it's maturity to really shine. He never was a leader and never had a game capable to consistently generate goals out of non chances like, dare i say, CR7 thanks to his physicality.
When things aren't going good and team isn't able to put Messi in spots where he has been the best ever, you won't see him jump over defenders and score from a random cross or corner. You won't see hum press down on defenders, win the ball and score out of nothing. You rarely seem him score screamers from 35 meters and give you a lead when the team couldn't dominate and create real dander.
Why does this matter? It matters because Messi still have 2 prime years in front of him and we have surrounded him with young players that are still learning and growing. In other words, we are forcing him to lose his time when he could be playing from some other squad like PSG or CITY that is clearly ahead of us.
In Messi's battle against CR7, Ronaldo best case is that he has proven himself as a winner in other situations while Messi never did so and had refused to even put himself in such position both because of low ambition but also because he has been faithful to the organization.
It would have been a CLASS ACT to have let him try his luck somewhere else while bagging 100 Millions € that would have allowed Bar?a to spend money on young star players in sync with the rest of the talent we have. And same goes IMO for Pique and Busquets. Those players are at the end of the line and i doubt they are mentally in the same place than 20 years old players that are from a different generation and no where in the same mental real at this point of their careers.
No one would actually mind to spend 1 season creating the bases for a new dominating foundation for the future. Most great teams that insist in holding to the past end up wasting money and years that could have been used in rebuilding.
Just my 2 cents on it.