3) OF Lane Thomas for Jon Lester (2021)
This is probably a more controversial take. Lester only pitched the remainder of 2021 for the Cardinals and then retired. Before the trade, Lester was far from endeared to St. Louis fans. He'd knocked the Cardinals out of the 2013 World Series with the Red Sox and had then guided the rival Cubs to the 2016 title. Lester wasn't even that great on the surface with St. Louis. He pitched to a 4.36 ERA over 66 innings. However, he did the most important thing that a pitcher could do. He won, and he won a lot.
When the Cardinals acquired Lester and J.A. Happ at the 2021 deadline, they were fading fast. They were on the verge of no longer being considered a contender. Jon Lester was a huge reason that they turned their season around. They went on to win an incredible 17 games in a row and punched their ticket to the postseason late in September after beating the Cubs. Lester went 4-1 as a Cardinal, and the team won seven of his final ten starts. He went at least five innings in eleven of his twelve starts as a Cardinal, and at no point let a game get completely out of hand. Lester did everything the Cardinals asked of him.
The return piece, Lane Thomas, has found success in Washington. He probably should have made an all-star team this season! His .805 OPS would fit nicely in the Cardinals lineup today. Except, he probably wouldn't be in the lineup. Thomas would not have started over Nootbaar or Walker. It's difficult to believe that the Cardinals would have given him opportunities instead of Tyler O'Neill, Dylan Carlson, and Alec Burleson. Thomas, at best, would have occupied the role of a fourth or fifth outfielder.
Considering the fact that Thomas would never have gotten a true opportunity to shine in St. Louis, this is a clear win-win deal. The Cardinals received short-term help and made the 2021 postseason. The Nationals received long-term help and now have a player who may be worth building around in Thomas. Thomas, for his part, received the chance to become a full-time player and has run with that opportunity. Lastly, Lester got one more chance to see October, though the Cardinals were knocked out in the Wild Card round.