With Messi's current age, it's just a matter of time before he decides to retire from the game and i think Barcelona were wise enough to think of the team Post Messi era and that's why they are re-signing Neymar and have brought in younger talents like Griezmann and Ousmane Dembele to ensure the future of their team.
Neymar messed up somewhere somehow. I don't even see him as Ballon D'or material. He is like one of those people who were so brilliant and had a very promising future when they were young, but then they let the limelight and fame distort there focus.
I also don't like his character sometimes on and off pitch. I mean the move to PSG was even never supposed to happen. If he wanted to become Messi's heir at Barcelona, he was just supposed to stay, learn from him then in a few years he would be the main man...but nah, Ney choose fame and money.
As for Ousmane Dembele, that kid is a loss for Barca. He will be loaned out a couple of times, and then he will leave after Barca realize he is just a liability