The problem has never been his quality or his performances. He's unparalleled as a player. But there's another dimension to being a leader, a captain apart from technical qualities, and that's being able to make your teammates believe in themselves, being able to pick them up when they are down, motivate them, inspire them. Messi has rarely done that. Even in that miraculous win against PSG, it was Neymar who was the spark that fueled that comeback. All the GOATS in other sports were just as capable as leaders as they were as players. Even when the Falcons were up 28-3, their own players knew it wasn't over because the other team had Brady. Same thing with Jordan. They had/have auras that made their teams always believe they were in the game, win or lose. Barca has collapsed too many times in the last decade to simply blame it on Valverde.
In 7 of the last 8 seasons, Barca didn't score a single away goal when they went out:
2012: 1:0 vs Chelsea
2013: 4:0 vs Bayern
2014: 1:0 vs Atletico
2016: 2:0 vs Atletico
2017: 3:0 vs Juventus
2018: 3:0 vs Roma
2019: 4:0 vs Liverpool
Yes, it's absolutely unfair to blame it on Messi. But we're talking about a GOAT candidate not a regular player or even a superstar. Different coaches, different players and yet Barca and Messi have been non-existent playing away. When the going gets tough, when Barca falls into a hole, Messi goes back to his shell, becomes lethargic and never displays leadership skills that vastly inferior players have displayed. Someone like a Puyol or Gattuso would have started kicking their teammates around once we went down 3:0. Messi is not that type and he never was. It's just who he is. It's a legitimate criticism especially coupled with the notion that his decade long rival, Ronaldo, while an inferior player, has won a lot more than he should have because he never heard the referee waive the fight off.