Barca were humiliated in Europe long before EV, 2013 Semifinals happened, losing 2 away games with 0-4 & 0-3 happened under Lucho too, losing to a vastly inferior Atletico happened before him twice too. Even Pep had a massive issue in the results of away games in comparison to home.
EV didn't fix that, but he wasn't the key to it. And neither was he given the authority to change things.
Look at Alonso and Madrid, ability to fix things is handed from the board to the manager, not the other way around
Yo people forget that. EV biggest problem was he couldnt calm down the players. Thats a big skill which Zidane and Ancelotti can do very well. In la liga pressure was much less so it was easy to dominate with EV's tactics. In CL you need to stay cool. Pep has also this problem thats why he only won 1 cl at City so far. Overall i think EV achieved much more than we expected, i mean we lost ll/cl to Real in 2017 + lost Ney. EV won 2 lls. Squad was also crap, looked great on paper but some players were already finished for top lvl.