#2)The clash of egos and playing styles
At the moment, the Barcelona playing XI is already filled with many senior superstars like Lionel Messi, Luis Suarez, Jordi Alba, Sergio Busquets and Gerard Pique. In such a situation, the arrival of Griezmann would add another superstar to the playing XI which could make things complicated from the management point of view.
With too many superstars, especially in the forward line, there is a massive chance that there could be a clash in egos which may not allow Griezmann to play at his best.
With the French national team and previously at Atletico Madrid, he was the main man of the team. While he is a pretty versatile attacker and can play anywhere across the front line, he usually likes to operate behind the main striker as a no.10 to link up the play, organize the attack and score goals or create chances at ease. However, Messi already operates in this role at Barcelona and it could be difficult for both left footers to play together (similar to Dybala's problems whilst operating with Messi).
Meanwhile, Gabriel Jesus is also a pretty versatile attacker and can play anywhere across the front line, and isn't much of a superstar compared to Griezmann.
While Gabriel he is a brilliant finisher, he is also an excellent passer of the ball, has an excellent first touch, can hold up play, can dribble through defences, and even move out wide at times to create space for other attackers. In short, he has all the qualities to become a striker with the 'Barca DNA'.
Moreover, he is still just 22 years old which means that he has enough time to mould himself into a 'Barca type no.9', which is not the same case with Griezmann.