There are two aspects to that.
The first aspect is that, yes, if you study tax avoidance associated with the use of tax havens, you will find that it is highly concentrated in the hands of a few very large multinational corporations. We are talking about thousands of multinationals, but that number is still low in relation to the large number of corporations in the world.
The second aspect is that once you give those large corporations a competitive advantage, because they have the opportunity to engage in tax avoidance, which means they are paying less in taxes than the others and their costs are lower than the others', you will be heightening those corporations' dominance. Because they are avoiding tax, those big corporations will get even bigger. So you will be increasing economic concentration in your economy. In the study I did with my co‑authors, we show that this is the case in certain sectors in the United States. The citation for the study is in the document I provided to you.