but one of his motivating factor to come to Barca was the fact that he was going to play with Messi,the world best player.
Yep, it may be one of his motivations to join Barcelona. But I think it shouldn't be the strongest motivation to be there.
now that Messi is no longer in the team,it would be even hard for Barca to even win a major tittle,because the team was built around Messi.
Don't too early judge Barca will be difficult to compete winning major trophies just because they have no longer Messi! Barcelona club should be bigger than Messi's name, they still have many top players with great taletented/skills on the squad.