There is a strong form and a weak form of the efficient market hypothesis. The weak form only says you can’t get above market returns through technical analysis studying past pricing and volume behavior or without insider knowledge because all public knowledge is already baked into the current price.
The strong form says you can not make above market returns, period, regardless of if you have insider knowledge or not, because even the insider knowledge is baked into the price already.
The efficient market hypothesis doesn’t say it will be a well performing market, only that you can’t make above market returns.
As a general rule it is indeed very difficult without insider knowledge to earn above market returns. Many have tried, few suceeds over the long term. Most dollar cost average because they know they can’t time the market.