The difference is that Sabathia would improve the Brewers, there's a good chance Ramirez would not. Assuming the most likely scenario where Ramirez replaces Hart, Rmairez's bat projects soem where between 2-3 wins better. That's huge. However, Braun is likely an average RFer causing the Brewers to lose half a win in RF from Hart. And Braun is a plus left fielder while Ramirez is abysmal, causing the Brewers to go from like +15 runs to -25. So unless the return for Hart is great, signing Ramirez makes the team worse.