The federal constitution isn't merely there to define the boundaries between state and federal jurisdiction; it's there to define the structure and powers of the federal government itself.

You're trying to argue that the federal government merely usurped powers that the state governments already had, and this is scarcely true. No state ever had unlimited regulatory authority, and no state ever had anything approaching "nearly unlimited police powers"; state constitutions are typically more explicit in restraining the exercise of power than even the federal constitution.