Messi won't necessarily be forced to be the main guy and put the team on his back though, they've won titles with their current core as it is. They've got enough talent around him to carry their own weight.
The not being a team player stuff is crazy to hear when he's coming off a season where he broke the league record for assists
He's been the best playmaker in the world for over a decade. He's also won most of his European titles when he wasn't the unquestioned leader and the gameplan wasn't centered around him so he can definitely have success as a contributor as well.
He has at least 2-3 seasons as a top 5 player in the world and a further couple of years as a quality supporting player if he chooses in my opinion