The team was much better before Messi signed. Neymar wasn't injured as much. Mbappe was in much better form; he's been pretty shit since the World Cup if we're being honest. Not to mention, they had a top manager in 2020.
They had 2 17-year-old players against Bayern in the 2nd leg. They had Ruiz and Vitinha in the midfield. Mbappe had a shit game. Messi was one of their best players in that 2nd leg.
In the first leg, they had a midfield of a 17-year-old, Soler, Pereira. Messi only came back from injury, and so did Mbappe.
Outside Mbappe, Messi, Neymar, Hakimi, and maybe Verratti, their squad is pretty average if we're being honest. Mendes and Marquinhos are decent, but I don't think they're top-class. And Ramos is about to be 37.
Look at the defense today for instance; Bernat, Pereira, and Bitshiabu are honestly shocking for a defense. They also had Ruiz and Pembele out there who are not good at all. By the way, Messi got a 7.8 rating today, so he was the least of their problems.
It isn't a coincidence that if you give Messi a balanced team with a decent midfield and defense... and with a decent coach, you'll win things. That's why he's won so much with Argentina in the past 2 years.