I think this is the hope, and Cocaine Mitch hasn't closed the door on witnesses. What he's trying to do is hold opening statements, a period of written questions, and then let the Senate decide what witnesses, if any, to call. That is what was done in 1999 with bipartisan agreement. I think it pissed him off that the House is trying to direct the trial by exercising a leverage that it actually doesn't have. It would be like a prosecutor telling a judge that he won't show up for trial unless the judge promises to make a favorable ruling on something before being formally asked. A judge would ignore something like that and dismiss a case if the prosecutor no-showed. That's what McConnell should do.
Frankly, there's nothing inherently wrong with calling witnesses if the Senate wants to hear directly from them. That's entirely their call. What's stupid is the idea that the House would deliberately not call certain witnesses that at least plausibly could provide damning evidence because it didn't want to make the effort, impeach without evidence, and then demand that the Senate go find the evidence that they didn't care to secure but that they tacitly admit is essential (and therefore tacitly admit that they did a horrendously crappy job and that, despite all the sanctimony and phony "solemnity," they didn't take their own role seriously). That's a chicken **** move, and he shouldn't honor it or take it remotely seriously.
Let's also bear in mind that Cocaine Mitch doesn't have any more authority on getting the testimony than the House had during the impeachment inquiry. If he subpoenas Bolton, Mulvaney, etc., the same executive privilege issues that the House ignored will have to be dealt with.