The argument of the article is that the journalists involved further investigated the transactions and determined that a lot were shady and that the regulators were failing to do their job ... or the banks were defying the regulators when the regulators were complaining. There was no claim of "every FinCEN proves a dirty deed" - it's explicit in the article.
The article makes a lot of bold claims that assume the truth of various unproven allegations. Journalists - who are paid to come up with dramatic sounding stories - are the exact opposite of the arbiters of truth when it comes to crime. Examples:
"people and companies tied to the massive looting of public funds in Malaysia"
Tied to? Tied by whom?
"more than $2 million for a young energy mogul’s company that has been accused of cheating"
Accused of? Accused by whom?
"amid a swirl of money laundering and corruption allegations spawning from his work with a pro-Russian political party in Ukraine."
A swirl of allegations? Alleged by whom? Additionally the article is filled with deceptive writing.
"In some cases the banks kept moving illicit funds even after U.S. officials warned them they’d face criminal prosecutions if they didn’t stop doing business with mobsters, fraudsters or corrupt regimes."
This sounds like the warnings were about specific mobsters/etc but it's carefully phrased to avoid claiming that. Yes, the USG tells banks to fight crime, everyone who ever opened a bank account knows that, this is not news.
"Suspicious activity reports reflect the concerns of watchdogs within banks and are not necessarily evidence of criminal conduct or other wrongdoing. Though a vast amount, the $2 trillion in suspicious transactions identified within this set of documents is just a drop in a far larger flood of dirty money"
One sentence after admitting that SARS aren't actual findings of criminal activity, they literally say that all those transactions are a part of "a flood of dirty money". They know that's not true! It's kind of sad, really. Journalism has reached the point where my first reaction to investigative journalists writing about leaked files is, "how are these liars going to BS me today?". It's a long way from the heydey of the Snowden leaks.