Wealth is made by labor, yes. But it is not accumulated by it. It's accumulated by being in a position of power whereby you can extract rents from the laborers who make it. In older times, this was done by threat of physical force. These days, it's more often done by exploiting some economic advantage - for example, if you own any valuable resource, such as land or means of production, you can extract rent from people who use it.

Whenever you see concentrated wealth with such extreme disparity that you have one person owning more than a million others, there are only two possible conclusions: either they really are a million times more productive, or it was actually produced by that million, and extracted from them via rents.

You could argue that those rents are fair, since they stem from legitimate ownership. But what makes it legitimate? Most land was originally taken by force, for example, and the result enshrined in law (that was written by the people who did this) post factum. If that doesn't make economic advantages that stem from such ownership unfair, then surely the same standard holds today, and those people have no right to complain if society decides to take it away from them by force, and enshrine it into law, just because it can.