€500m went out of the club and into his pockets in just 4 years. Barca have a debt of around €1.2 billion - net debt around €0.5 billion, I believe.
His fee of €2.5m per week was the benchmark for many other extortionate contracts.
Their main issue right now is (a) their debt and (b) their wage to turnover ratio. Other causes - including COVID, particularly - important just as obscene contracts like Messi which, themselves, took a significant chunk.
His wages ALONE contributing to about 20-25% of the wage to turnover % - meaning with a cap of 70% and his salary constituting 20-25%. we're talking about 30-35% of that wage cap being assigned to just one player.
Then there are knock on ramifications vis a vis contract negotiations with other players. See Griezmann, in particular. Agents will use contracts exactly like Messi's as benchmarks. Griezmann is on an obscene contract too, around €700-800K per week and Coutinho on €500K per week. The benchmark for these contract negotiations are most definitely Messi's contract.
It's called "breaking the wage structure" and Messi's obscene income per week of around €2.5m per week (including annual loyalty bonus + signing on fee) most definitely broke the wage structure as well as putting a tremendous strain on the debt of the club.