A council review in 2014 of progress on the economic development strategy identified the Auckland Global brand as a priority. The council subsequently instructed Ateed to carry out the work through Ateed's statement of intent.
Auckland councillor Dick Quax blasted the move as "outrageous raping of the ratepayer" and councillor Chris Fletcher said it was "a complete waste of money".
In response O'Riley said each councillor was interviewed as part of the project, including Quax.
"Only a small minority declined to take part."
O'Riley said claims 115 people worked on creating the slogan were not true.
"Ateed does not have 115 people working on this project. The internal project team comprises three people ... it is disingenuous to claim that council staff who attended a one-hour brainstorming session are working on the project."
O'Riley admitted the $500,000 cost on "development of the draft Auckland Story over a two-year period" was accurate.
"We believe that the costs incurred are reasonable given the large scope of this work and the need to engage a wide range of Aucklanders and stakeholders in this work," O'Riley said.
"This compares favourably to the $2 million that was spent by centralGovernment developing the 'New Zealand Story', and amounts expended by other cities on similar activity."
The city's proposed new global brand - The Place Desired by Many - was worked on by three project staff over two years, while 115 council staff attended workshops.
Reaction to the branding exercise has been mostly negative.
Act leader David Seymour slammed it, and offered some alternatives of his own.
"The place where my kids will afford a home before I die, the place where I'm not stuck in traffic all the time, the place where my consents get processed within the 20-day statutory requirement, the place where my rates bear some resemblance to services rendered."
Seymour said if the newly elected council "cannot refocus the bureaucracy on things that matter to Aucklanders, Parliament will have to clip their wings by amending the Local Government Act to do it for them".
Ngati Whatua Orakei Trust expressed disappointment over the "proposed slogan", and the Auckland Ratepayers' Alliance called it "the most expensive two-word translation in the history of Auckland".
And away from the City of Sails, mayors have also ripped into the exercise, with Grey District Mayor Tony Kokshoorn saying the cost to come up with it was "patently ridiculous".
Herald readers also lashed out against it.
"Not only a complete, and certainly not-required, waste of council's time and ratepayers' money, but one of the worst city slogans in history," wrote Barry Brown.
Jewele McLeod summed the situation up with "If you didn't laugh, you'd cry".
Others questioned why the city's branding needed to be changed at all.
"What on earth is wrong with 'Auckland The City of Sails'?" Rob Morton asked.