It would be more fair to say that economics assumes that people try to achieve their goals in rational ways. Which is actually a fairly good assumption in most cases when people can work in large groups, face the same challenges again and again, and can watch each other succeed or fail. There's really no assumption that people are equally informed, because when I read economists talking about things they always seem to spend at least a quarter of their time talking about signalling.

Sometimes the assumption that people are rational breaks down, like with sticky prices caused by what psychologists would call "loss aversion". In that case economists make the changes they need to to their models to account for how people differ from the simplest model. This is basically how you get the entire field of Macroeconomics.