4.) Yelich wouldn't be that big of an improvement over the Cubs OF. The have pretty much 2+ WAR at each OF position.
Yelich is close to twice that, a borderline MVP candidate, and is currently playing for one of the Cubs' top rivals. Without him, the Brewers would be buried. With him, the Cubs would lead the Cardinals by a couple more games.
Of course, with Chili Davis as the hitting coach, Yelich would've been encouraged to not take advantage of his more HR friendly ballpark in the most homer friendly era of MLB history. So maybe he wouldn't have helped that much.