That's a flaw, said Veron. “It makes the system less robust,” he said, calling it a necessary political compromise. “It was the price to pay to move forward. I think the glass is more than half full.”

Veron said the new measure will probably capture about 70-80 percent of the eurozone banking system by assets, including all of Europe's big banks such as France's BNP Paribas, Germany's Deutsche Bank and Italy's UniCredit. It will also probably cover many larger regional banks such as Germany's local state banks and the trouble-prone Spanish savings banks.

The ECB can on paper intervene in any bank, but would leave the day-to-day supervision of smaller ones to local authorities, raising questions about how effective supervision would be.

Ahead lies hard bargaining over a resolution authority. Leaders have also debated the exact conditions for banks getting money directly from the European bailout fund – in essence, having taxpayers all over Europe finance the cleanup of individual countries' financial disasters. As things stand, Spain and Ireland are still stuck with the debts they ran up bailing out banks. Some countries argue the ESM could be tapped only after national treasuries, leaving the bank-government link at least partly still in place.

Eurasia Group analyst Mujtaba Rahman said the new supervisor by itself won't sever the link between governments and banks because “member states are still on the hook” for bailouts. Yet, the step is “absolutely an improvement compared to the starting point. None of this infrastructure existed before.”

“It doesn't help with this crisis. It helps with the next one.”