Coutinho wasn't faultless for his flop at Barca, but the coach was mainly responsible.
Put him in a role that fit him terribly. He's a playmaker first and foremost. Needs players a head of him to link up with. At Barca he was basically tasked with either going past players on his own or running deep, both of which are hard when your not a quick guy.
A few times, out of necessity, he was put back into a 10 role and he instantly came alive. His creativity, ability to navigate tight spaces and shooting became applicaple in a different way. But next game, it was back out wide. Now, Griezmann is suffering under the same clueless managing, while an overweight, burned out Suarez that hasn't been himself since the 15/16 season is hogging is position.