Westpac chief executive Brian Hartzer agrees with his counterparts at NAB and Commonwealth Bank that there's no need for the competition watchdog to supervise the banks, insisting he's already trying to "compete our competitors into oblivion".
Mr Hartzer, the last of the big four bosses to front the House of Representatives economics committee, said there are already two active regulators mandated to oversee competition in the sector.
"Although there are many assertions about competition in the industry, my own personal experience is it is highly competitive," he told MPs in Canberra.
"We spend all day thinking about how we compete our competitors into oblivion and avoid having the same happening to us."
It was put to Mr Hartzer that Australian Competition and Consumer Commission chairman Rod Sims believed competition between the big lenders was not as intense as it might be.
"That's not the way it feels when you run a bank," Mr Hartzer said.
The heads of CBA and NAB also used their appearances before the same committee to dismiss the need for additional oversight from the ACCC.
The ACCC can investigate suspected one-off breaches of competition law - such as when it took action against ANZ and Macquarie Bank over alleged cartel-like behaviour - but has no mandate for systemic oversight.
Unlike his peers, ANZ boss Shayne Elliott this week said he had no objection to the ACCC gaining additional powers, but still shot down suggestions customers could be best served by a royal commission.
He said it was easier and quicker to tackle problems on an issue-by-issue basis.
Mr Hartzer also brushed off the need for a royal commission - pointing out that banks are already being pursued by regulators over various instances of suspected wrongdoing.
He denied the corporate regulator's allegation that Westpac breached its duty to act in the best interests of customers when it recommended they join the bank's poorly performing BT Financial superannuation fund.
He said a disclaimer made it clear to customers his bank was only providing "general advice" on switching super.
"It's a balanced fund that's designed to deliver returns through cycles in different markets that, while it might be appropriate for some, it might be inappropriate for others," Mr Hartzer told MPs.
"But in a general advice conversation, there's a limit to the extent to which you can take that into account."
If the Australian Securities and Investments Commission won its federal court case against Westpac over the issue, Mr Hartzer said, it would "effectively be close to impossible to provide general advice".
He also said he was keen on the idea of opening up customer data to rivals, with the aim of stoking competition, but said he was wary about exposing them to the risk of financial fraud.
"We're relatively agnostic about who leads the process. We are supportive of open data ... (but) our obligations to protect customer data to protect them from fraud and all that are very real," he said.
