You're literally twisting words to avoid dealing with an inherent weakness of anarchy. Roosevelt did not create a monopoly. Even if you twist the meaning of monopoly to include government, it already existed. Even if it did, a monopoly can prevent OTHER monopolies from forming. So you have one "monopoly" if you use your twisted definition, rather than all industries being monopolies. You're avoiding the real issue:

How can anarchy prevent monopolies from forming?