A while back I wrote about some of the problems with any plan to repeal the Direct Election of Senators. There are a few other problems with the approach.
It brings the flaws of the electoral college system to another branch of government, creating a certainty that you’ll have people in office who didn’t win the popular vote. An infamous example occurred in Abraham Lincoln’s 1858 Senate race against Stephen Douglas. More people voted Republican, but Douglas was still the choice of the state legislature, because the census hadn’t caught up with changes in population.
It also increases partisanship. Character matters in direct elections, which allows for impressive politicians to win in states in which their party is weak. This would include Republicans like Susan Collins of Maine and Democrats like Heidi Heitkamp of North Dakota or Jon Tester of Montana.
It creates more rewards for gerrymandering. As geographic sorting favors Republican, it might help the party, but it will hurt the democracy.
I can appreciate that some state legislatures flipped recently in states where you would expect one party to have been powerful for some time, although that would probably have happened sooner if it was understood that control of the state legislature was tantamount to the election of their chosen party hack to the Senate.