Coutinho was thought of as a very good player, but he didnt really start to take that step into world class territory until his last half season at Liverpool. He had 12 goals and 8 assists in 19 combined champions league and premier league appearances as Barcelona were trying to negotiate a transfer for him.
He very much looked world class during that stretch. However, it was also pretty obvious that their offense was flowing through him as a CAM in a way that it wouldn't at Barcelona.
He's worth big money to a club that wants to use him like Liverpool were at the end there. Maybe not 100 million pounds, but easily 75 or 80.
As mentioned by others already, Barcelona just panicked and bought the biggest stars they could to replace Neymar, not considering fit.
As a Liverpool fan, I don't blame him for wanting to go to Barcelona, as playing for a Spanish giant is the dream for every South American kid. And I don't even really blame him for forcing the transfer as that's the only way Liverpool were going to sell him. However, the paths both clubs have taken should not be a huge surprise to him.
There was a clear confidence that fall within the club that they were on the verge of big things, and he was the centerpiece of the attack, even with Salah starting to put up big numbers. Even when he was sold, fans weren't as upset as they were when Suarez left.
And even though Barcelona has not done as well as most would've accepted, it was already pretty clear with the Neymar fiasco and Dembele's slow start that all was not well there. And with Messi there, Coutinho should've known he was going there to play a supporting role. I do feel sorry for him, and I'm not delighting in his struggles, but I do wonder what he was expecting to happen when he made the switch.