Bezos becoming richer through stock gains costs me nothing, because his wealth increase is purely speculative. He didn't take that billions out of the economy, or from the poor, or from anyone.

So I think this is not a good measurement of whether or not the majority have become richer or poorer. A much better measurement is do they have more stuff, or better stuff, or a higher quality of life than before. This is the level I think most people care about. Not whether some rich people got richer (mostly from stock growth) faster than I did.

Apart from most of the small book shops in the world going out of business?

Why did they go out of business? Probably because they offered worse prices and worse service. By taking less money from his customers, Bezos makes his customers richer than if they shopped somewhere else. The few business owners who are affected and are made worse off are rounding error and do not change the fact that the median person is better off.