You seem to be asking your second question rhetorically, but its actually an interesting question. The reason we call anti-monopolistic activity "anti-trust" is because Standard Oil organized itself as a series of companies related only through a common trust. That trust controlled 40 different companies, and was the original target of the government's ire. When the trust was ordered dissolved, it eventually was replaced by a holding company.

The history is interesting and informative, and explains a lot about why the US government started to care about issues of corporate governance in the first place. When people talk today about the dangers of "monopoly," they often misunderstand the point entirely.

Size alone is not the issue. It never has been.