McMahon has an elevated BABIP this season. His metrics are the best of his career, but are you really going to trade for a player on an outlier season, with a single elevated statistic that accounts for the only real difference in his batting line from when he has been a 90 wRC+ hitter, with only 1 guaranteed year of control?
If the Cubs want to go after Soto or Vlad, they are going to have to think outside the box at 3B. The options are very uninspirational. That's why I've brought up Ronny Mauricio. Others have brought up Eguy Rosario. The Cubs are going to have to find their Joey Ortiz.
The options at catcher are even worse. I truly dont have a clue what the Cubs do there. The chances guys like O'Hoppe and Langelliers get moved are slim to none. The best options seem to be ones that wont be starting the season on the MLB roster, like Ford from the Mariners or Teel from the Red Sox. But then you are talking strictly about the highly coveted prospect that works out on average like 10% of the time. Are the Royals willing to trade Fermin, given that Perez is still around for another year and 2 of their top 10 prospects are catchers? Or maybe you target one of those prospects and ask about Carter Jensen who just got promoted to AA and gets good marks on his defense and eye at the plate, though his bat sounds to be pretty passive similar to Ian Happ when he started. Danny Jansen has 2 straight years of regression and this season has lost 5 MPHs on his max exit velocity from his good years. He's turning into the catching version of a Paredes himself and he's not that great of a defensive catcher, so if he can't hit for power any more then what good is he? I truly dont have a damn clue what to do at catcher. Going the prospect route seems to be the best option.