A theory behind busting trusts is that monopolies stifle innovation, and thus growth, in the long term. When it comes to "competing with China" (which, to be naive, I'm not sure the meaning of), many nationally competing firms will have a better result for future consumers than if there were a single "national champion."
Here is an hour long video where Lina Khan makes this point to the Council on Foreign Relations much more cogently than I can: https://www.youtube.com/live/L_QaZk5iJOA?is=rk192CuSIBHLemsi