Perhaps you're right; perhaps 1-2% of people (if that) could potentially beat the market in their investments. And the majority of people think they're in that 1-2%.

Meanwhile, index funds have the lovely advantage that you can't do worse than the market.

If you have extra energy to spend investigating investments, use it to diversify into a handful of minimal-overhead index funds rather than just one. And if you fancy yourself an investor as a hobby, take a small fraction of your savings and play with it, and congratulate yourself if you manage to do better than "buy high and sell low".

But in general, most people would greatly improve the status of their investments by just throwing the whole thing into a halfway decent index fund. That's the most sensible general advice when talking to a large audience of people; get them there first, which takes far less effort, and then let people who really think they can do better attempt to do so.