Don't disagree with your general summation of him. He's absolutely a luxury player but if he was more consistent, turning up in say 6-7/10 games rather than 3-4 at best, he's a luxury a lot of elite clubs would like to have.
I think they'd rather have another attacker to make the difference up front. Would Barcelona rather have Ousmane Dembelé/Griezmann on the pitch with Messi and Suarez, or another player who's job is to keep possession (who'd be pretty redundant in 90% of games)?