Force India's Sergio Perez was the only driver outside Mercedes, Ferrari and Red Bull to finish a grand prix in the top three in this year's 21 races, the Mexican ending up third in Azerbaijan in April.
Canadian Lance Stroll, for Williams, was in the same position at the same Baku circuit in 2017, when the season had 20 races.
"Two podiums from a total of 123 is unacceptable, especially when it comes with an ever increasing technical and financial divide," Brawn said in a Formula One season review after last Sunday's closing Abu Dhabi Grand Prix.
"It’s a problem we are tackling together with the (governing) FIA and the teams, because the future of Formula One depends on it," added the Briton, who was previously a technical director of Ferrari and principal of Mercedes.
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Mercedes, Ferrari and Red Bull are also the only teams to have won a Formula One race since the current V6 turbo hybrid engines were introduced in 2014.
Sunday was the 100th grand prix of that era and Lewis Hamilton, now a five times world champion, has won 51 of them for Mercedes. Hamilton also won 11 races this year, leading 458 of the season's 1,264 laps.
German driver Nico Hulkenberg, who races for the Renault works team and was 'best of the rest' in seventh place overall this year, has now started 156 grands prix without once standing on the podium.
Brawn said seven of the 10 teams were effectively racing in their own championship.
"There are various solutions on the table and we must all accept that we can’t go on like this for too much longer," said Brawn.
"I don’t mean to cause offence by referring to the 'other' championship, it’s just a way of describing the situation and their battle was certainly thrilling. However, it’s hard for the fans to truly get excited about a battle for eighth place."
The top three places in the constructors' championship were decided before the season-ender, with Mercedes winning both titles for the fifth year in a row.
The rules are being tweaked for 2019, with aerodynamic changes aimed at making it easier for drivers to follow cars and battle on track, ahead of a more substantial overhaul planned for 2021.
The top teams are already working hard to limit the impact on performance, however, and have far bigger budgets to play with than the smaller teams.
"The downforce is basically being set back by a year or more, and we have to compensate," Mercedes team boss Toto Wolff said at the weekend.
"But there is a bunch of really, really clever people who are looking at the regulations and trying to find ways of having a lot of downforce on the car and I’m curious to see whether those cars are really going to be slower next year or not."
(Reporting by Alan Baldwin; editing by Ken Ferris)
