It would be naive to think that it did not have any advantage because of its position in the financial industry.
Having only one losing trading day in a quarter could not be accomplished without insider information.
in dislocated markets, making markets is actually relatively easy, so it's not that surprising that they usually don't lose money. they also have hundreds of traders. each one of them probably had many losing days, but in aggregate, they have good traders and systems, so they rarely have losing days now.
also, how do you know that it's impossible without insider information? what reason do you have to back up your claim?
GS has turned into a giant hedge fund. And their numbers are consistently better than any other fund or investor. Better than Warren Buffet or George Soros. They're impossibly good.
Most of this is from computers trading >billion shares per day.
I know traders who think that many price moves in the market are due to insider trading they're not privy to. Since every trader, to my knowledge, seems to think this--even the ones at big investment banks--it's hard to say whether it's superstition or not, but it doesn't stop them from being profitable with only "outsider information".
In fact there are a few who actually are BIGGER brokers who serve more institutional clients than GS...