Great.
By your logic then, no appointment should be made until the American people have decided which party will control congress in five weeks.
The fact the Senate Majority Leader has the ability to block a vote, because enough Americans have elected Senators in his party, or that caucus with his party, is a fact. It doesn't matter when the election occurs, the Senate Majority Leader can decide what gets voted on , at any time during their term, because they are the Senate Majority Leader.
If the Democrats, or other Senators that caucus with the Democrats, win enough seats in Congress during the Fall Elections, they could then be the Majority. At that point, If they win the Majority, they can decide on a Senate Majority Leader, who will then have the power to determine what's brought to the Senate floor for a vote.
We aren't talking about if's, could's and should's. We are talking about who actually has the power to do something based on how many Americans have voted one way or another, and it's a fact, no matter what your logic is.