How did the 17th Amendment change the equilibrium of power in the national government?
When the Constitution was written, the election of senators to represent the states in the new Congress was delegated to the legislatures of the respective states. This method of electing senators was devised in recognition of the perceived need of the states to have a means of direct representation and reflected attitudes of many of the Founding Fathers that did not believe common citizens had the education or responsibility to be trusted with being involved in the government.
The 17th Amendment changed this procedure by mandating direct election of senators by voters from each individual state. The change in procedure came in response to charges that some senatorial positions had been obtained as a result of corrupt relationships between candidates and members of state legislatures, and because some legislatures had reached deadlock and were unable to elect a senator.
Whether this is a positive or negative change is an opinion. You will need to consider the evidence and decide what you believe, then determine how you will support your decision.