There is a lot of conjecture in your arguments - how Barca would have performed in the absence of Messi, no-one can say with certainty.
Theoretically, the €550mm could have been spent to bring in additional players and achieve similar success. Not saying, it would have happened but it’s a possibility. It’s also possible that Coutinho / Griezman may have settled better.
I have been watching Barca from before Messi ever played for them and they have always been a top 3 global club. Success in the current era started with the emergence of Ronaldinho, and others like Iniesta, Xavi, Henry, Busquets, Villa and many others contributed to it. I haven’t read the Athletic article but I know enough about business and finance to understand that there is no way to segregate how much one “player” brought in. It’s one or couple of journalists view. If someone links the article, I am happy to go through it and change my mind.