Yes, I've thought about this problem with Democracy as well. On the other hand, even if you have, for example, a monarchy or oligarchy, you still have to rely on how well the monarch or oligarchs are informed. And monarchs and oligarchs are susceptible to the same types of bad advice than anyone else is. And in fact, the systems for spreading bad advice to monarchs and oligarchs would, I imagine, actually be pretty similar to the systems for spreading bad advice to an electorate, with vested power structures working behind the scenes to sew disinformation at lots of levels, including the education system itself.

So I'm not actually sure if having a single decision maker actually increases your chances of having better educated decisions. But at least with a democracy, everyone gets to say what they think they want (even if what they think they want is misinformed). And that is probably a good thing in itself.