See the figures for last year. There is still plenty of money left from Brasileirão, Libertadores, Sudamericana and especially Copa do Brasil this year. Atlético-MG won almost twice as much as Palmeiras in prizes, Corinthians won almost as much as Palmeiras too. Yet both Atlético-MG and Corinthians are still absolute shit. In fact, despite winning more than twice as much in prizes as Fluminense did, Atlético-MG still made less money than them last year.
Club budgets are much more complicated than prizes. It goes from ticket and merch sales, to broadcasting rights, to sponsorship deals, to membership fees, to a whole range of other things. Flamengo are extremely profitable with or without the CWC, Botafogo have Textor's money either way, Palmeiras too has very stable and robust sources of revenue. Fluminense is the only club that benefits significantly from this.
Even then, there is nothing stopping Corinthians, Cruzeiro or even São Paulo from becoming financially competitive with these four aside from blatant mismanagement and corruption.