The people are represented in the House. With the Senate also elected by popular vote, we have 2 chambers focused on vote grabbing through entitlements.
With a Senate beholden to a State legislator, the Senate would be beholden to the state. Since the state governments also want power, it becomes a balance between state and federal.
The problem of the imbalance of power between the State and Federal government is mostly through an expansive reading of the interstate commerce clause.
So long as THAT is interpreted in the way it is, States have almost no power not subject to Federal oversight/regulation, and it doesn't matter one wit which way Senators were elected.