Europe’s bankers defended the big bank model this week in Davos as the mounting cost of regulation puts a question mark over its future. JPMorgan, the biggest U.S. bank by assets, has faced growing pressure to consider a break-up, and similar questions are being put to less profitable European rivals such as Deutsche Bank, Barclays and Credit Suisse . JPMorgan Chief Executive Jamie Dimon last week said splitting his bank would be bad for the financial prestige of the United States, and he won support from his peers at this week’s World Economic Forum in Davos.