Hamilton is leaving McLaren at the end of the year after a six-year spell at the Woking team to race alongside Nico Rosberg at Mercedes from next season.
The Briton admitted ahead of the season finale in Brazil that the Interlagos race may have been his last chance to win a race for a while given Mercedes's current form.
The Brackley-based outfit won the Chinese Grand Prix earlier this year but then struggled to keep up with its rivals and endured a five-race point-less streak in the championship run-in.
Despite that, Brawn believes Mercedes has all the ingredients to fight back and is not ruling out competing at the front.
"I hope so," Brawn said when asked by AUTOSPORT if Hamilton's predictions were too pessimistic.
"Obviously we're working very hard to give both him and Nico the opportunity to win and take pole positions. That's our ambition, our objective.
"It's obviously critical we improve from where we are. We're going to try [even] if we don't hit all our objectives next year. You never know what other people will do.
"I'd like to think we can do a few things of those things next year.
"I think Lewis was just playing things down. I'm sure in his heart he wants to win and set pole positions, but he understands the journey we've got to go on."
Brawn reckons the 2008 world champion's quality and input will also provide Mercedes with a significant boost.
"We're very excited about the prospect of working with Lewis," he said. "It's going to be very interesting for all of us. I'm sure he'll be different to Michael.
"The team are very excited that we're still able to have a driver of that calibre. As we get a stronger car, obviously the drivers will become even more critical for us."
Hamilton is under contract with McLaren until the end of the year, meaning he cannot start work with his new team until 2013.
Brawn is optimistic that such delays will not affect Hamilton's transition to his new environment, adding: "It's not a big problem.
"There are obviously things that you start to do. You start to build the relationship with the engineers, and that can start in earnest in January."