how would having state legislatures select senators be better than direct election by the people?
State legislators are people who represent vastly smaller numbers of people than Congressmen. They have to look those they represent in the eye, quite regularly. Giving them back the power to pick Senators, as the Founders intended, would return massive amounts of power to the states. Senators were supposed to represent the states, and the House was meant to represent the people directly. The 17th Amendment fouled that up, and basically gave us a House and a super-House. The states suffered the consequences.