It would be the real downfall of Barca if you try to build around Griezmann. Guy cant dribble or shoot and is not used to the possession style and tight spaces. He is more suited for the pragmatic style of France and Atletico, where he can put his workrate to use. In Barca, its more about offensive capabilities.
Griezmann is extremely limited in this area, people might think he is some kind of special player who tracks back and defend, but overall his cons outweighs his pros. Even Neymar as a main man in Barca has more potential. Griezmann should go to a different team, that uses his skillset more. If Griezmann was so good attacking wise clubs like City will be after him but only we are the one who thinks he is a good signing. France was just incredibly stacked with Mbappe and Pogba carrying the team more. He never won the CL anyway, and the World cup was just a one off. For me, he is a somewhat decent second striker who makes use of set pieces and loose balls to fluff up his stats, in reality he is extremely conservative and deficient. I mean, it's not like we haven't seen him struggled without Messi as well.
He wouldnt play significantly better unless we massively alter our style to be like Atletico 2.0. It's really not that easy being a main man at Barca as many claimed. Building a team also requires the right profile and man for the job, not just based solely on numbers of goals and assists, because his playmaking and dribbling is absolutely atrocious.
I agree though Messi should leave with this clown of a board, but to think some players or the team will play better without him is an overstatement.