As I recall, one argument for the 17th was that some/many Senators were bought and paid for by special interests bribing key members of state legislatures and that ‘bribing’ a whole state’s electorate would be financially impossible. And of course it would be much more ‘democratic’.
I think that history has shown the first argument to be false—by dumping lots of money into an election Senators are still bought and paid for. What it did do, of course is change the very structure of American Federalism. Senators were originally in place to represent state governments, not the people. That’s why Senators get to vote on treaties. And it is why states are equally represented in the Senate—a feature that leftists still decry.
There was corruption in the appointment/election of Senators pre the 17th amendment, but the popular election of them has been far more destructive IMHO